feat: 标签页 IndexedDB 持久化 + 最近打开文件

1. 标签页持久化（关闭后恢复）：
   - tabStore 新增 loadFromDB/saveToDB 方法
   - 启动时从 IndexedDB 加载标签页快照
   - 标签页增删改时异步保存到 IndexedDB
   - 关闭窗口后重新打开，所有标签页自动恢复

2. 最近打开文件：
   - 欢迎屏幕显示最近打开的 10 个文件
   - 点击文件名直接打开
   - 从侧边栏/对话框/主进程打开文件时自动记录
   - 文件路径显示在文件名下方（灰色小字）
   - hover 高亮效果

REFACTOR-PLAN.md 实现进度更新：
  ✅ CodeMirror 6 编辑器
  ✅ 格式化工具栏
  ✅ 标签页 IndexedDB 持久化
  ✅ 最近打开文件 UI
  ✅ Zustand stores
  ✅ TypeScript 全量类型
  ✅ unified/rehype
  ✅ electron-vite
  ❌ CSS Modules（全局 CSS 已足够）

src/renderer/stores/tabStore.ts

@@ -1,11 +1,13 @@
 import { create } from 'zustand'
 import { nanoid } from 'nanoid'
 import type { Tab } from '../types/tab'
+import { tabRepository } from '../db/tabRepository'
 
 interface TabState {
   tabs: Tab[]
   activeTabId: string | null
   mruStack: string[]
+  _loaded: boolean
 
   createTab: (filePath?: string | null, content?: string) => Tab
   closeTab: (tabId: string) => void
@@ -18,16 +20,69 @@ interface TabState {
   getActiveTab: () => Tab | null
   getTabIndex: (tabId: string) => number
   updateTabScroll: (tabId: string, scroll: Partial<Pick<Tab, 'scrollTop' | 'scrollLeft' | 'selectionStart' | 'selectionEnd' | 'previewScrollTop'>>) => void
+  loadFromDB: () => Promise<void>
+  saveToDB: () => Promise<void>
 }
 
-// L-04: 使用 nanoid 替代计数器（HMR 安全）
 export const useTabStore = create<TabState>((set, get) => ({
   tabs: [],
   activeTabId: null,
   mruStack: [],
+  _loaded: false,
+
+  // 从 IndexedDB 加载标签页快照
+  loadFromDB: async () => {
+    if (get()._loaded) return
+    try {
+      const snapshots = await tabRepository.loadAll()
+      if (snapshots.length > 0) {
+        const tabs: Tab[] = snapshots.map(s => ({
+          id: s.id,
+          filePath: s.filePath,
+          content: s.content,
+          isModified: s.isModified,
+          scrollTop: s.scrollTop,
+          scrollLeft: s.scrollLeft,
+          selectionStart: s.selectionStart,
+          selectionEnd: s.selectionEnd,
+          previewScrollTop: s.previewScrollTop
+        }))
+        set({
+          tabs,
+          activeTabId: tabs[tabs.length - 1].id,
+          _loaded: true
+        })
+      } else {
+        set({ _loaded: true })
+      }
+    } catch {
+      set({ _loaded: true })
+    }
+  },
+
+  // 保存当前标签页到 IndexedDB
+  saveToDB: async () => {
+    const { tabs } = get()
+    if (tabs.length === 0) {
+      await tabRepository.clearAll()
+      return
+    }
+    const snapshots = tabs.map(t => ({
+      id: t.id,
+      filePath: t.filePath,
+      content: t.content,
+      isModified: t.isModified,
+      scrollTop: t.scrollTop,
+      scrollLeft: t.scrollLeft,
+      selectionStart: t.selectionStart,
+      selectionEnd: t.selectionEnd,
+      previewScrollTop: t.previewScrollTop,
+      updatedAt: Date.now()
+    }))
+    await tabRepository.saveAll(snapshots)
+  },
 
   createTab: (filePath = null, content = '') => {
-    // 检查是否已打开
     if (filePath) {
       const existing = get().tabs.find(t => t.filePath === filePath)
       if (existing) {
@@ -53,6 +108,9 @@ export const useTabStore = create<TabState>((set, get) => ({
       activeTabId: tab.id
     }))
 
+    // 异步保存
+    setTimeout(() => get().saveToDB(), 0)
+
     return tab
   },
 
@@ -69,7 +127,6 @@ export const useTabStore = create<TabState>((set, get) => ({
         if (newTabs.length === 0) {
           newActiveId = null
         } else {
-          // M-05: 优先从 MRU 栈取最近使用的标签
           const mruCandidate = newMru.find(id => newTabs.some(t => t.id === id))
           if (mruCandidate) {
             newActiveId = mruCandidate
@@ -87,22 +144,22 @@ export const useTabStore = create<TabState>((set, get) => ({
         mruStack: newMru
       }
     })
+
+    setTimeout(() => get().saveToDB(), 0)
   },
 
   closeOtherTabs: (tabId) => {
     set(state => {
       const target = state.tabs.find(t => t.id === tabId)
       if (!target) return state
-      return {
-        tabs: [target],
-        activeTabId: tabId,
-        mruStack: []
-      }
+      return { tabs: [target], activeTabId: tabId, mruStack: [] }
     })
+    setTimeout(() => get().saveToDB(), 0)
   },
 
   closeAllTabs: () => {
     set({ tabs: [], activeTabId: null, mruStack: [] })
+    setTimeout(() => get().saveToDB(), 0)
   },
 
   closeTabsToRight: (tabId) => {
@@ -119,6 +176,7 @@ export const useTabStore = create<TabState>((set, get) => ({
         mruStack: state.mruStack.filter(id => newTabs.some(t => t.id === id))
       }
     })
+    setTimeout(() => get().saveToDB(), 0)
   },
 
   switchToTab: (tabId) => {
@@ -127,10 +185,7 @@ export const useTabStore = create<TabState>((set, get) => ({
       const newMru = state.activeTabId
         ? [state.activeTabId, ...state.mruStack.filter(id => id !== state.activeTabId)]
         : state.mruStack
-      return {
-        activeTabId: tabId,
-        mruStack: newMru
-      }
+      return { activeTabId: tabId, mruStack: newMru }
     })
   },