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/Editor/Editor.tsx

@@ -22,7 +22,8 @@ export function Editor({ darkMode }: EditorProps) {
     getScrollTop,
     setScrollTop,
     getSelection,
-    setSelection
+    setSelection,
+    setLineAtTop
   } = useCodeMirror({
     content: activeTab?.content ?? '',
     onChange: useCallback((value: string) => {
@@ -31,11 +32,24 @@ export function Editor({ darkMode }: EditorProps) {
       setModified(activeTabId, true)
     }, [activeTabId, updateTabContent, setModified]),
     darkMode,
-    onScroll: useCallback((ratio: number) => {
-      window.dispatchEvent(new CustomEvent('editor-scroll', { detail: { ratio } }))
+    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 } }))
     }, [])
   })
 
+  // 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

@@ -11,7 +11,7 @@ interface UseCodeMirrorOptions {
   content: string
   onChange: (value: string) => void
   darkMode: boolean
-  onScroll?: (ratio: number) => void
+  onScroll?: (line: number) => void
 }
 
 export function useCodeMirror({ content, onChange, darkMode, onScroll }: UseCodeMirrorOptions) {
@@ -64,13 +64,17 @@ export function useCodeMirror({ content, onChange, darkMode, onScroll }: UseCode
 
     viewRef.current = view
 
-    // 滚动事件监听
+    // 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 maxScroll = dom.scrollHeight - dom.clientHeight
-        const ratio = maxScroll > 0 ? dom.scrollTop / maxScroll : 0
-        onScroll(ratio)
+        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)
@@ -127,13 +131,24 @@ export function useCodeMirror({ content, onChange, darkMode, onScroll }: UseCode
     view.focus()
   }, [])
 
-  // 滚动到指定位置
+  // 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,
@@ -143,6 +158,7 @@ export function useCodeMirror({ content, onChange, darkMode, onScroll }: UseCode
     setScrollTop,
     getSelection,
     setSelection,
-    scrollTo
+    scrollTo,
+    setLineAtTop
   }
 }