feat(checkpoint): 添加 Checkpoint 可视化管理功能

Core 层增强:
- 添加 safety.ts: 7点安全检查机制
- 添加 session-tracker.ts: 会话级检查点跟踪
- 添加 lock.ts: 并发控制文件锁
- 添加 lfs.ts: Git LFS 大文件支持
- 添加 path-validator.ts: 路径验证
- 添加 commit-message.ts: 智能提交消息生成
- 增强 manager.ts: 支持三种恢复模式、unrevert 撤销回滚

Server 层:
- 添加 checkpoints.ts: 16个 REST API 端点
  - GET/POST /checkpoints: 列表/创建检查点
  - GET/DELETE /checkpoints/🆔 获取/删除检查点
  - GET /checkpoints/:id/diff: 获取差异
  - POST /checkpoints/:id/restore: 恢复到检查点
  - POST /checkpoints/unrevert: 撤销回滚
  - GET /checkpoints/:id/safety-check: 安全检查

UI 层:
- 添加 CheckpointPanel.tsx: 检查点列表面板
- 添加 CheckpointDiffViewer.tsx: 差异查看器
- 添加 RestoreDialog.tsx: 恢复确认对话框
- 添加 16 个 API 客户端函数
- 添加完整的 TypeScript 类型定义

Web/Desktop 集成:
- 添加 History 按钮到工具栏
- 集成 CheckpointPanel 组件

packages/web/src/App.tsx

@@ -13,6 +13,7 @@ import {
   MCPPanel,
   HooksPanel,
   AgentsPanel,
+  CheckpointPanel,
   Toaster,
   listSessions,
   createSession,
@@ -29,6 +30,7 @@ export function App() {
   const [showMCP, setShowMCP] = useState(false);
   const [showHooks, setShowHooks] = useState(false);
   const [showAgents, setShowAgents] = useState(false);
+  const [showCheckpoints, setShowCheckpoints] = useState(false);
   const [sessionTitleUpdate, setSessionTitleUpdate] = useState<{ sessionId: string; name: string } | null>(null);
 
   // 初始化：加载或创建会话
@@ -117,6 +119,7 @@ export function App() {
               onOpenMCP={() => setShowMCP(true)}
               onOpenHooks={() => setShowHooks(true)}
               onOpenAgents={() => setShowAgents(true)}
+              onOpenCheckpoints={() => setShowCheckpoints(true)}
             />
           ) : (
             <div className="flex-1 flex items-center justify-center h-full">
@@ -177,6 +180,9 @@ export function App() {
       {/* Agents 面板 */}
       {showAgents && <AgentsPanel onClose={() => setShowAgents(false)} responsive />}
 
+      {/* Checkpoints 面板 */}
+      {showCheckpoints && <CheckpointPanel onClose={() => setShowCheckpoints(false)} responsive />}
+
       {/* 移动端底部文件按钮 */}
       <button
         onClick={() => setShowFileBrowser(true)}