feat: 重写滚动同步为 VS Code 方案（data-line + 二分查找）

核心变更：
- 新增 rehypeSourceLine 插件：利用 unified AST position 信息，
  给渲染后的块级元素注入 data-line 属性，标记源文件行号
- 重写 scrollSync.ts：用二分查找替代正则匹配 identifyBlockStarts，
  精确映射行号→预览 DOM 位置，线性插值填充行间偏移
- useCodeMirror.ts：onScroll 从 ratio 改为行号派发，
  使用 CodeMirror 的 lineBlockAtHeight 精确计算当前行
- Preview.tsx：双向同步（编辑器→预览 + 预览→编辑器）
- Editor.tsx：监听 preview-scroll 事件实现反向同步

原理：与 VS Code Markdown 预览滚动同步方案一致
- 渲染时：AST position → data-line 属性
- 滚动时：二分查找 [data-line] 元素 → 线性插值滚动位置

src/renderer/components/Preview/Preview.tsx

@@ -1,6 +1,7 @@
 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('')
@@ -23,28 +24,49 @@ 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
+  // 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 ratio = (e as CustomEvent).detail?.ratio ?? 0
-      const panel = previewRef.current?.parentElement
-      if (!panel || isSyncingRef.current) return
+      const line = (e as CustomEvent).detail?.line
+      if (typeof line !== 'number') return
 
-      isSyncingRef.current = true
-      const maxScroll = panel.scrollHeight - panel.clientHeight
-      panel.scrollTop = ratio * maxScroll
-      // 下一帧重置标志
-      requestAnimationFrame(() => { isSyncingRef.current = false })
+      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')