feat: v4.0.0 大版本升级 - SQLite3 + ReAct Agent

- P0: 存储层 IndexedDB → SQLite3 (better-sqlite3)，7张表 + FTS5全文搜索
- P1: Agent Engine 升级为 ReAct 模式（思考→行动→观察→反思）
- P2: 新增 4 个工具（memory_search, memory_add, session_list, session_read）
- P3: 上下文管理器（滑动窗口 + 摘要压缩 + 记忆注入）
- P4: UI 改版（ReAct 执行面板样式 + 思考过程卡片）
- P5: IndexedDB → SQLite 数据迁移支持
- MAX_LOOPS 10→15, MAX_LOOP_TIME 5min→10min, 错误自动重试 2 次

src/main/preload.ts

@@ -43,6 +43,30 @@ contextBridge.exposeInMainWorld('metonaDesktop', {
   onMainLog: (callback: (data: { level: string; message: string; detail?: string }) => void) => {
     ipcRenderer.on('main:log', (_: unknown, data: { level: string; message: string; detail?: string }) => callback(data));
   },
+  db: {
+    saveSession: (session: unknown) => ipcRenderer.invoke('db:saveSession', session),
+    getSession: (id: string) => ipcRenderer.invoke('db:getSession', id),
+    getAllSessions: () => ipcRenderer.invoke('db:getAllSessions'),
+    deleteSession: (id: string) => ipcRenderer.invoke('db:deleteSession', id),
+    clearAllSessions: () => ipcRenderer.invoke('db:clearAllSessions'),
+    saveMessage: (msg: unknown) => ipcRenderer.invoke('db:saveMessage', msg),
+    getMessages: (sessionId: string) => ipcRenderer.invoke('db:getMessages', sessionId),
+    saveMemory: (entry: unknown) => ipcRenderer.invoke('db:saveMemory', entry),
+    getMemory: (id: string) => ipcRenderer.invoke('db:getMemory', id),
+    getAllMemories: () => ipcRenderer.invoke('db:getAllMemories'),
+    getMemoriesByType: (type: string) => ipcRenderer.invoke('db:getMemoriesByType', type),
+    deleteMemory: (id: string) => ipcRenderer.invoke('db:deleteMemory', id),
+    clearAllMemories: () => ipcRenderer.invoke('db:clearAllMemories'),
+    searchMemories: (query: string, limit?: number) => ipcRenderer.invoke('db:searchMemories', query, limit),
+    saveSetting: (key: string, value: unknown) => ipcRenderer.invoke('db:saveSetting', key, value),
+    getSetting: (key: string, defaultValue?: unknown) => ipcRenderer.invoke('db:getSetting', key, defaultValue),
+    saveToolCall: (tc: unknown) => ipcRenderer.invoke('db:saveToolCall', tc),
+    getToolCalls: (sessionId: string) => ipcRenderer.invoke('db:getToolCalls', sessionId),
+    saveTrace: (trace: unknown) => ipcRenderer.invoke('db:saveTrace', trace),
+    getTraces: (sessionId: string) => ipcRenderer.invoke('db:getTraces', sessionId),
+    exportSessions: () => ipcRenderer.invoke('db:exportSessions'),
+    importSessions: (data: unknown) => ipcRenderer.invoke('db:importSessions', data),
+  },
   workspace: {
     getDir: () => ipcRenderer.invoke('workspace:getDir'),
     setDir: (dir: string) => ipcRenderer.invoke('workspace:setDir', dir),