refactor: 删除分屏功能 + 代码审计修复 + 安全加固

## 删除分屏功能
- 删除 ViewMode 'split' 类型，仅保留 editor/preview
- 删除 splitRatio 状态和 Resizer 组件
- 删除滚动同步模块 (scrollSync.ts, rehypeSourceLine.ts)
- 更新快捷键: Ctrl+1 编辑, Ctrl+2 预览

## Bug 修复
- 修复 Toast setTimeout 内存泄漏 (App.tsx)
- 修复 ModifiedBanner reload 更新错误标签 (改用 modifiedFilePath 匹配)
- 修复 FileWatcher error 未重置 isSelfWriting (file-watcher.ts)
- 修复另存为时未 stop watcher (ipc-handlers.ts)

## 死代码清理 (10 项)
- 删除 main/ipc-channels.ts (与 shared/ 重复)
- 删除 main/file-system.ts 未使用的 formatBytes
- 删除 constants.ts 6 个未使用常量
- 删除 fileUtils.ts 未使用的 formatBytes
- 删除 Icons.tsx 5 个未使用图标 (SplitView/ChevronUp/ChevronDown/X/ArrowUp/ArrowDown)
- 删除 useCodeMirror 未使用的 getContent/scrollTo
- 删除 TabBar 未使用的 menuRef
- 删除 Tab.scrollLeft/previewScrollTop 字段
- 删除 tabStore 未使用的 getTabIndex
- 删除 Toast/ModifiedBanner 多余 React import

## 安全加固
- ipc-handlers: 添加路径遍历防护 (validatePath 函数)
- preload: openExternal 仅允许 http/https 协议
- window-manager: 启用 sandbox: true
- preload: removeAllListeners 改为精确取消订阅 (返回 Unsubscribe 函数)

## 状态持久化
- activeTabId 持久化到 IndexedDB (刷新后恢复正确标签)
- sidebar 状态持久化到 IndexedDB (isVisible/sidebarWidth)

## 代码优化
- preload 使用 IPC_CHANNELS 常量替代硬编码字符串
- ipc-handlers _event 类型改为 IpcMainInvokeEvent
- settingsRepository 删除 splitRatio 字段

src/renderer/components/Editor/Editor.tsx

@@ -22,8 +22,7 @@ export function Editor({ darkMode }: EditorProps) {
     getScrollTop,
     setScrollTop,
     getSelection,
-    setSelection,
-    setLineAtTop
+    setSelection
   } = useCodeMirror({
     content: activeTab?.content ?? '',
     onChange: useCallback((value: string) => {
@@ -31,25 +30,9 @@ export function Editor({ darkMode }: EditorProps) {
       updateTabContent(activeTabId, value)
       setModified(activeTabId, true)
     }, [activeTabId, updateTabContent, setModified]),
-    darkMode,
-    onScroll: useCallback((line: number) => {
-      // 派发行号给预览侧做滚动同步
-      window.dispatchEvent(new CustomEvent('editor-scroll', { detail: { line } }))
-    }, [])
+    darkMode
   })
 
-  // 反向同步：监听预览滚动事件
-  useEffect(() => {
-    const handlePreviewScroll = (e: Event) => {
-      const line = (e as CustomEvent).detail?.line
-      if (typeof line === 'number') {
-        setLineAtTop(Math.floor(line) + 1) // setLineAtTop 是 1-indexed
-      }
-    }
-    window.addEventListener('preview-scroll', handlePreviewScroll)
-    return () => window.removeEventListener('preview-scroll', handlePreviewScroll)
-  }, [setLineAtTop])
-
   // 切换标签时加载内容
   useEffect(() => {
     if (!activeTab) return

src/renderer/components/Editor/useCodeMirror.ts

@@ -11,10 +11,9 @@ interface UseCodeMirrorOptions {
   content: string
   onChange: (value: string) => void
   darkMode: boolean
-  onScroll?: (line: number) => void
 }
 
-export function useCodeMirror({ content, onChange, darkMode, onScroll }: UseCodeMirrorOptions) {
+export function useCodeMirror({ content, onChange, darkMode }: UseCodeMirrorOptions) {
   const containerRef = useRef<HTMLDivElement>(null)
   const viewRef = useRef<EditorView | null>(null)
   const isExternalUpdate = useRef(false)
@@ -81,23 +80,7 @@ export function useCodeMirror({ content, onChange, darkMode, onScroll }: UseCode
 
     viewRef.current = view
 
-    // 滚动事件监听：派发行号（支持小数表示行内偏移）
-    const handleScroll = () => {
-      if (onScroll) {
-        const dom = view.scrollDOM
-        const scrollTop = dom.scrollTop
-        const block = view.lineBlockAtHeight(scrollTop)
-        const line = view.state.doc.lineAt(block.from)
-        const fraction = block.height > 0
-          ? (scrollTop - block.top) / block.height
-          : 0
-        onScroll(line.number - 1 + Math.max(0, fraction))  // 0-indexed + 行内比例
-      }
-    }
-    view.scrollDOM.addEventListener('scroll', handleScroll)
-
     return () => {
-      view.scrollDOM.removeEventListener('scroll', handleScroll)
       view.destroy()
       viewRef.current = null
     }
@@ -116,12 +99,6 @@ export function useCodeMirror({ content, onChange, darkMode, onScroll }: UseCode
       isExternalUpdate.current = false
     }
   }, [])
-
-  // 获取当前内容
-  const getContent = useCallback(() => {
-    return viewRef.current?.state.doc.toString() ?? ''
-  }, [])
-
   // 获取/设置滚动位置
   const getScrollTop = useCallback(() => {
     return viewRef.current?.scrollDOM.scrollTop ?? 0
@@ -147,35 +124,13 @@ export function useCodeMirror({ content, onChange, darkMode, onScroll }: UseCode
     view.dispatch({ selection: { anchor: from, head: to } })
     view.focus()
   }, [])
-
-  // 滚动到指定行
-  const scrollTo = useCallback((pos: number) => {
-    const view = viewRef.current
-    if (!view) return
-    view.dispatch({ effects: EditorView.scrollIntoView(pos, { y: 'center' }) })
-  }, [])
-
-  // 滚动使指定行出现在编辑器顶部（反向同步用）
-  const setLineAtTop = useCallback((lineNumber: number) => {
-    const view = viewRef.current
-    if (!view) return
-    const line = Math.max(1, Math.min(lineNumber, view.state.doc.lines))
-    const lineInfo = view.state.doc.line(line)
-    const block = view.lineBlockAt(lineInfo.from)
-    const currentTop = view.lineBlockAtHeight(view.scrollDOM.scrollTop).top
-    view.scrollDOM.scrollTop += block.top - currentTop
-  }, [])
-
   return {
     containerRef,
     viewRef,
     setContent,
-    getContent,
     getScrollTop,
     setScrollTop,
     getSelection,
-    setSelection,
-    scrollTo,
-    setLineAtTop
+    setSelection
   }
 }

src/renderer/components/Icons.tsx

@@ -58,19 +58,6 @@ export function Save({ size = defaultProps.size }: IconProps) {
   )
 }
 
-export function SplitView({ size = defaultProps.size }: IconProps) {
-  return (
-    <svg width={size} height={size} viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="1.75" strokeLinecap="round" strokeLinejoin="round">
-      <rect x="3" y="3" width="18" height="18" rx="3"/>
-      <line x1="12" y1="3" x2="12" y2="21"/>
-      <rect x="5" y="7" width="5" height="2" rx="1" fill="currentColor" opacity="0.4"/>
-      <rect x="5" y="11" width="3" height="2" rx="1" fill="currentColor" opacity="0.3"/>
-      <rect x="14" y="7" width="5" height="2" rx="1" fill="currentColor" opacity="0.4"/>
-      <rect x="14" y="11" width="3" height="2" rx="1" fill="currentColor" opacity="0.3"/>
-    </svg>
-  )
-}
-
 export function EditMode({ size = defaultProps.size }: IconProps) {
   return (
     <svg width={size} height={size} viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="1.75" strokeLinecap="round" strokeLinejoin="round">
@@ -175,32 +162,6 @@ export function FolderPlus({ size = 14 }: IconProps) {
   )
 }
 
-// ===== 搜索栏图标 =====
-export function ChevronUp({ size = 12 }: IconProps) {
-  return (
-    <svg width={size} height={size} viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2.5" strokeLinecap="round" strokeLinejoin="round">
-      <polyline points="18 15 12 9 6 15"/>
-    </svg>
-  )
-}
-
-export function ChevronDown({ size = 12 }: IconProps) {
-  return (
-    <svg width={size} height={size} viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2.5" strokeLinecap="round" strokeLinejoin="round">
-      <polyline points="6 9 12 15 18 9"/>
-    </svg>
-  )
-}
-
-export function X({ size = 14 }: IconProps) {
-  return (
-    <svg width={size} height={size} viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round">
-      <line x1="18" y1="6" x2="6" y2="18"/>
-      <line x1="6" y1="6" x2="18" y2="18"/>
-    </svg>
-  )
-}
-
 // ===== 拖拽覆盖层图标 =====
 export function UploadCloud({ size = 64 }: IconProps) {
   return (
@@ -213,25 +174,6 @@ export function UploadCloud({ size = 64 }: IconProps) {
   )
 }
 
-// ===== 箭头/导航图标 =====
-export function ArrowUp({ size = 12 }: IconProps) {
-  return (
-    <svg width={size} height={size} viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2.5" strokeLinecap="round" strokeLinejoin="round">
-      <line x1="12" y1="19" x2="12" y2="5"/>
-      <polyline points="5 12 12 5 19 12"/>
-    </svg>
-  )
-}
-
-export function ArrowDown({ size = 12 }: IconProps) {
-  return (
-    <svg width={size} height={size} viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2.5" strokeLinecap="round" strokeLinejoin="round">
-      <line x1="12" y1="5" x2="12" y2="19"/>
-      <polyline points="19 12 12 19 5 12"/>
-    </svg>
-  )
-}
-
 // ===== 欢迎屏幕图标 =====
 export function WelcomeFile({ size = 20 }: IconProps) {
   return (

src/renderer/components/ModifiedBanner/ModifiedBanner.tsx

@@ -1,5 +1,3 @@
-import React from 'react'
-
 interface ModifiedBannerProps {
   onReload: () => void
   onDismiss: () => void

src/renderer/components/Preview/Preview.tsx

@@ -1,13 +1,11 @@
 import React, { useState, useEffect, useCallback, useRef } from 'react'
 import { useTabStore } from '../../stores/tabStore'
 import { renderMarkdown } from '../../lib/markdown'
-import { scrollPreviewToLine, getLineAtScrollOffset, invalidateScrollCache } from '../../lib/scrollSync'
 
 export function Preview() {
   const [html, setHtml] = useState('')
   const previewRef = useRef<HTMLDivElement>(null)
   const requestIdRef = useRef(0)
-  const isSyncingRef = useRef(false)
 
   const activeTabId = useTabStore(s => s.activeTabId)
   const tabs = useTabStore(s => s.tabs)
@@ -24,49 +22,10 @@ export function Preview() {
     renderMarkdown(activeTab.content, activeTab.filePath).then(result => {
       if (requestId === requestIdRef.current) {
         setHtml(result)
-        invalidateScrollCache()
       }
     })
   }, [activeTabId, activeTab?.content])
 
-  // 滚动同步：监听编辑器滚动事件（VS Code 方案：行号 → 二分查找）
-  useEffect(() => {
-    const handleEditorScroll = (e: Event) => {
-      const line = (e as CustomEvent).detail?.line
-      if (typeof line !== 'number') return
-
-      const container = previewRef.current?.parentElement
-      if (!container || isSyncingRef.current) return
-
-      scrollPreviewToLine(line, container, isSyncingRef)
-    }
-
-    window.addEventListener('editor-scroll', handleEditorScroll)
-    return () => window.removeEventListener('editor-scroll', handleEditorScroll)
-  }, [])
-
-  // 反向同步：预览滚动 → 通知编辑器
-  useEffect(() => {
-    const container = previewRef.current?.parentElement
-    if (!container) return
-
-    const handleScroll = () => {
-      if (isSyncingRef.current) return
-
-      const line = getLineAtScrollOffset(container.scrollTop, container)
-      if (line !== null) {
-        isSyncingRef.current = true
-        window.dispatchEvent(new CustomEvent('preview-scroll', { detail: { line } }))
-        requestAnimationFrame(() => {
-          isSyncingRef.current = false
-        })
-      }
-    }
-
-    container.addEventListener('scroll', handleScroll, { passive: true })
-    return () => container.removeEventListener('scroll', handleScroll)
-  }, [activeTabId])
-
   // 拦截链接点击
   const handleClick = useCallback((e: React.MouseEvent) => {
     const link = (e.target as HTMLElement).closest('a')

src/renderer/components/Sidebar/Sidebar.tsx

@@ -74,12 +74,10 @@ export function Sidebar() {
 
   useEffect(() => {
     if (!window.electronAPI) return
-    window.electronAPI.onDirChanged(() => {
+    const unsubscribe = window.electronAPI.onDirChanged(() => {
       refreshTree()
     })
-    return () => {
-      window.electronAPI?.removeAllListeners('sidebar:dirChanged')
-    }
+    return unsubscribe
   }, [refreshTree])
 
   useEffect(() => {

src/renderer/components/TabBar/TabBar.tsx

@@ -1,4 +1,4 @@
-import React, { useCallback, useState, useEffect, useRef } from 'react'
+import React, { useCallback, useState, useEffect } from 'react'
 import { useTabStore } from '../../stores/tabStore'
 import { getFileName } from '../../lib/fileUtils'
 import { Close, Plus } from '../Icons'
@@ -21,7 +21,6 @@ export function TabBar() {
   const closeTabsToRight = useTabStore(s => s.closeTabsToRight)
 
   const [menu, setMenu] = useState<ContextMenuState>({ visible: false, x: 0, y: 0, tabId: '' })
-  const menuRef = useRef<HTMLDivElement>(null)
 
   const handleClose = useCallback((e: React.MouseEvent, tabId: string) => {
     e.stopPropagation()
@@ -133,8 +132,7 @@ export function TabBar() {
       {/* 右键菜单 */}
       {menu.visible && (
         <div
-          ref={menuRef}
-          className="tab-context-menu"
+          className="tab-context-menu" 
           style={{ left: menu.x, top: menu.y }}
           onClick={(e) => e.stopPropagation()}
         >

src/renderer/components/Toast/Toast.tsx

@@ -1,5 +1,3 @@
-import React from 'react'
-
 interface ToastProps {
   message: string
 }

src/renderer/components/Toolbar/Toolbar.tsx

@@ -1,11 +1,11 @@
 import React from 'react'
-import { FolderOpen, Save, SplitView, EditMode, PreviewMode, Moon, Sun } from '../Icons'
+import { FolderOpen, Save, EditMode, PreviewMode, Moon, Sun } from '../Icons'
 
 interface ToolbarProps {
   onOpen: () => void
   onSave: () => void
-  viewMode: 'split' | 'editor' | 'preview'
-  onViewModeChange: (mode: 'split' | 'editor' | 'preview') => void
+  viewMode: 'editor' | 'preview'
+  onViewModeChange: (mode: 'editor' | 'preview') => void
   darkMode: boolean
   onToggleDark: () => void
 }
@@ -23,15 +23,11 @@ export function Toolbar({ onOpen, onSave, viewMode, onViewModeChange, darkMode,
           <span>保存</span>
         </button>
         <div className="toolbar-divider" />
-        <button className={`toolbar-btn ${viewMode === 'split' ? 'active' : ''}`} onClick={() => onViewModeChange('split')} title="编辑+预览 (Ctrl+1)">
-          <SplitView size={18} />
-          <span>分屏</span>
-        </button>
-        <button className={`toolbar-btn ${viewMode === 'editor' ? 'active' : ''}`} onClick={() => onViewModeChange('editor')} title="纯编辑 (Ctrl+2)">
+        <button className={`toolbar-btn ${viewMode === 'editor' ? 'active' : ''}`} onClick={() => onViewModeChange('editor')} title="编辑 (Ctrl+1)">
           <EditMode size={18} />
           <span>编辑</span>
         </button>
-        <button className={`toolbar-btn ${viewMode === 'preview' ? 'active' : ''}`} onClick={() => onViewModeChange('preview')} title="纯预览 (Ctrl+3)">
+        <button className={`toolbar-btn ${viewMode === 'preview' ? 'active' : ''}`} onClick={() => onViewModeChange('preview')} title="预览 (Ctrl+2)">
           <PreviewMode size={18} />
           <span>预览</span>
         </button>