fix: 实现编辑器-预览滚动同步

问题: 分屏模式下编辑器滚动时，预览面板不跟随滚动。

实现:
- Editor handleScroll 计算滚动比例，派发 editor-scroll 自定义事件
- Preview 监听 editor-scroll 事件，按比例设置 preview-panel scrollTop
- isSyncingRef 防止双向循环触发

原理: 编辑器 scrollTop / (scrollHeight - clientHeight) = 预览 scrollTop / (scrollHeight - clientHeight)

src/renderer/components/Editor/Editor.tsx

@@ -118,13 +118,18 @@ export function Editor() {
     }, 150)
   }, [getActiveTab, updateTabContent, setModified, updateLineNumbers, updateFileSizeDisplay])
 
-  // 滚动同步
+  // 滚动同步：通知 Preview 跟随滚动
   const handleScroll = useCallback(() => {
     const textarea = textareaRef.current
     if (!textarea) return
+    // 行号跟随
     if (lineNumbersRef.current) {
       lineNumbersRef.current.scrollTop = textarea.scrollTop
     }
+    // 计算滚动比例，派发给 Preview
+    const maxScroll = textarea.scrollHeight - textarea.clientHeight
+    const ratio = maxScroll > 0 ? textarea.scrollTop / maxScroll : 0
+    window.dispatchEvent(new CustomEvent('editor-scroll', { detail: { ratio } }))
   }, [])
 
   // Tab 键支持

src/renderer/components/Preview/Preview.tsx

@@ -6,12 +6,13 @@ 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)
   const activeTab = tabs.find(t => t.id === activeTabId) ?? null
 
-  // B-03 + M-07: 响应式渲染（无轮询，无竞态）
+  // 响应式渲染（无轮询，无竞态）
   useEffect(() => {
     if (!activeTab) {
       setHtml('')
@@ -20,13 +21,30 @@ export function Preview() {
 
     const requestId = ++requestIdRef.current
     renderMarkdown(activeTab.content, activeTab.filePath).then(result => {
-      // M-07: 只有当 requestId 仍为最新时才更新
       if (requestId === requestIdRef.current) {
         setHtml(result)
       }
     })
   }, [activeTabId, activeTab?.content])
 
+  // 滚动同步：监听编辑器滚动事件
+  useEffect(() => {
+    const handleEditorScroll = (e: Event) => {
+      const ratio = (e as CustomEvent).detail?.ratio ?? 0
+      const panel = previewRef.current?.parentElement
+      if (!panel || isSyncingRef.current) 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 })
+    }
+
+    window.addEventListener('editor-scroll', handleEditorScroll)
+    return () => window.removeEventListener('editor-scroll', handleEditorScroll)
+  }, [])
+
   // 拦截链接点击
   const handleClick = useCallback((e: React.MouseEvent) => {
     const link = (e.target as HTMLElement).closest('a')