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/desktop/src/App.tsx

@@ -11,6 +11,7 @@ import {
   MCPPanel,
   HooksPanel,
   AgentsPanel,
+  CheckpointPanel,
   Toaster,
   listSessions,
   createSession,
@@ -27,6 +28,7 @@ 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
@@ -101,6 +103,7 @@ 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">
@@ -136,6 +139,9 @@ export function App() {
       {/* Agents 面板 */}
       {showAgents && <AgentsPanel onClose={() => setShowAgents(false)} />}
 
+      {/* Checkpoints 面板 */}
+      {showCheckpoints && <CheckpointPanel onClose={() => setShowCheckpoints(false)} />}
+
       {/* Toast 通知 */}
       <Toaster />
     </div>

packages/desktop/src/pages/Chat.tsx

@@ -3,7 +3,7 @@
  */
 
 import { useEffect, useRef } from 'react';
-import { WifiOff, MessageSquare, Settings, FolderOpen, Terminal, Plug, Zap, Bot } from 'lucide-react';
+import { WifiOff, MessageSquare, Settings, FolderOpen, Terminal, Plug, Zap, Bot, History } from 'lucide-react';
 import { motion, AnimatePresence } from 'framer-motion';
 import {
   useChat,
@@ -24,6 +24,7 @@ interface ChatPageProps {
   onOpenMCP?: () => void;
   onOpenHooks?: () => void;
   onOpenAgents?: () => void;
+  onOpenCheckpoints?: () => void;
 }
 
 export function ChatPage({
@@ -36,6 +37,7 @@ export function ChatPage({
   onOpenMCP,
   onOpenHooks,
   onOpenAgents,
+  onOpenCheckpoints,
 }: ChatPageProps) {
   const {
     messages,
@@ -129,8 +131,21 @@ export function ChatPage({
           <ConnectionStatus />
 
           {/* 工具栏按钮 */}
-          {(onOpenConfig || onToggleFileBrowser || onOpenCommands || onOpenMCP || onOpenHooks || onOpenAgents) && (
+          {(onOpenConfig || onToggleFileBrowser || onOpenCommands || onOpenMCP || onOpenHooks || onOpenAgents || onOpenCheckpoints) && (
             <div className="flex items-center gap-1.5 border-l border-gray-600 pl-3">
+              {/* Checkpoints 按钮 */}
+              {onOpenCheckpoints && (
+                <motion.button
+                  whileHover={{ scale: 1.1 }}
+                  whileTap={{ scale: 0.9 }}
+                  onClick={onOpenCheckpoints}
+                  className="p-1.5 rounded-lg text-gray-400 hover:text-gray-200 hover:bg-gray-700 transition-colors"
+                  title="Checkpoints"
+                >
+                  <History size={20} />
+                </motion.button>
+              )}
+
               {/* Agents 按钮 */}
               {onOpenAgents && (
                 <motion.button