feat(commands): 实现命令 CRUD 完整功能

Core:
- 新增 CommandManager 类，支持创建、更新、删除命令
- 验证命令名称防止路径遍历攻击
- 自动生成 Markdown 文件（含 YAML frontmatter）
- 内置命令保护（不可修改/删除）

Server:
- POST /api/commands - 创建命令
- GET /api/commands/:name/content - 获取命令完整内容
- PUT /api/commands/:name - 更新命令
- DELETE /api/commands/:name - 删除命令

UI:
- 新增 createCommand、updateCommand、deleteCommand、getCommandContent 函数
- 新增 CreateCommandInput、UpdateCommandInput、CommandContent 类型

packages/core/src/index.ts

@@ -33,8 +33,16 @@ export { SessionStorage } from './session/storage.js';
 export type { SessionData, SessionSummary } from './session/types.js';
 
 // Commands
-export { getCommandRegistry, createCommandExecutor } from './commands/index.js';
-export type { Command, CommandInput, CommandExecutionResult } from './commands/index.js';
+export { getCommandRegistry, createCommandExecutor, createCommandManager } from './commands/index.js';
+export type {
+  Command,
+  CommandInput,
+  CommandExecutionResult,
+  CreateCommandInput,
+  UpdateCommandInput,
+  CommandContent,
+  CommandOperationResult,
+} from './commands/index.js';
 
 const program = new Command();