fix: 修复 markdown 编辑保存后内容丢失的问题

- 在 saveContent 中缓存 unsavedContent，避免 async 期间的竞态条件
- 在 useMarkdownLogic 中添加 lastContentRef 跟踪内容变化，防止不必要的编辑器更新

src/stores/tabStore.ts

@@ -331,7 +331,9 @@ export const useTabStore = create<TabStore>((set, get) => {
       const isAsyncImportProcessing = isAsyncImportProcessingContent(tab.content)
       if (isAsyncImportProcessing) return
 
-      await saveFileContent(filePath, tab.unsavedContent)
+      const contentToSave = tab.unsavedContent
+
+      await saveFileContent(filePath, contentToSave)
 
       set((state) => {
         const newTabs = new Map(state.tabs)
@@ -339,7 +341,8 @@ export const useTabStore = create<TabStore>((set, get) => {
         if (currentTab) {
           newTabs.set(filePath, {
             ...currentTab,
-            content: currentTab.unsavedContent,
+            content: contentToSave,
+            unsavedContent: contentToSave,
             isEditing: false,
           })
         }