feat: 添加后台 Agent 执行和模型选择功能

- 新增 AgentManager 管理后台 Agent 生命周期
- Task 工具支持 run_in_background 参数实现后台执行
- Task 工具支持 model 参数选择 sonnet/opus/haiku 模型
- 新增 agent_output 工具查询后台 Agent 执行状态和结果
- 添加 AgentManager 和 AgentOutput 工具单元测试

package.json

@@ -36,6 +36,7 @@
     "js-yaml": "^4.1.1",
     "ora": "^8.1.0",
     "tree-sitter-bash": "^0.25.1",
+    "uuid": "^13.0.0",
     "vscode-jsonrpc": "^8.2.1",
     "vscode-languageserver-protocol": "^3.17.5",
     "web-tree-sitter": "^0.25.10",
@@ -44,6 +45,7 @@
   "devDependencies": {
     "@types/js-yaml": "^4.0.9",
     "@types/node": "^22.0.0",
+    "@types/uuid": "^10.0.0",
     "@vitest/coverage-v8": "^4.0.15",
     "tsx": "^4.19.0",
     "typescript": "^5.6.0",