feat(mcp): implement unified MCP management for v3.7.0

BREAKING CHANGE: Migrate from app-specific MCP storage to unified structure

## Phase 1: Data Structure Migration
- Add McpApps struct with claude/codex/gemini boolean fields
- Add McpServer struct for unified server definition
- Add migration logic in MultiAppConfig::migrate_mcp_to_unified()
- Integrate automatic migration into MultiAppConfig::load()
- Support backward compatibility through Optional fields

## Phase 2: Backend Services Refactor
- Completely rewrite services/mcp.rs for unified management:
  * get_all_servers() - retrieve all MCP servers
  * upsert_server() - add/update unified server
  * delete_server() - remove server
  * toggle_app() - enable/disable server for specific app
  * sync_all_enabled() - sync to all live configs
- Add single-server sync functions to mcp.rs:
  * sync_single_server_to_claude/codex/gemini()
  * remove_server_from_claude/codex/gemini()
- Add read_mcp_servers_map() to claude_mcp.rs and gemini_mcp.rs
- Add new Tauri commands to commands/mcp.rs:
  * get_mcp_servers, upsert_mcp_server, delete_mcp_server
  * toggle_mcp_app, sync_all_mcp_servers
- Register new commands in lib.rs

## Migration Strategy
- Detects old structure (mcp.claude/codex/gemini.servers)
- Merges into unified mcp.servers with apps markers
- Handles conflicts by merging enabled apps
- Clears old structures after migration
- Saves migrated config automatically

## Known Issues
- Old commands still need compatibility layer (WIP)
- toml_edit type conversion needs fixing (WIP)
- Frontend not yet implemented (Phase 3 pending)

Related: v3.6.2 -> v3.7.0

src-tauri/src/commands/mcp.rs

@@ -143,3 +143,53 @@ pub async fn sync_enabled_mcp_to_gemini(state: State<'_, AppState>) -> Result<bo
 pub async fn import_mcp_from_gemini(state: State<'_, AppState>) -> Result<usize, String> {
     McpService::import_from_gemini(&state).map_err(|e| e.to_string())
 }
+
+// ============================================================================
+// v3.7.0 新增：统一 MCP 管理命令
+// ============================================================================
+
+use crate::app_config::McpServer;
+
+/// 获取所有 MCP 服务器（统一结构）
+#[tauri::command]
+pub async fn get_mcp_servers(
+    state: State<'_, AppState>,
+) -> Result<HashMap<String, McpServer>, String> {
+    McpService::get_all_servers(&state).map_err(|e| e.to_string())
+}
+
+/// 添加或更新 MCP 服务器
+#[tauri::command]
+pub async fn upsert_mcp_server(
+    state: State<'_, AppState>,
+    server: McpServer,
+) -> Result<(), String> {
+    McpService::upsert_server(&state, server).map_err(|e| e.to_string())
+}
+
+/// 删除 MCP 服务器
+#[tauri::command]
+pub async fn delete_mcp_server(
+    state: State<'_, AppState>,
+    id: String,
+) -> Result<bool, String> {
+    McpService::delete_server(&state, &id).map_err(|e| e.to_string())
+}
+
+/// 切换 MCP 服务器在指定应用的启用状态
+#[tauri::command]
+pub async fn toggle_mcp_app(
+    state: State<'_, AppState>,
+    server_id: String,
+    app: String,
+    enabled: bool,
+) -> Result<(), String> {
+    let app_ty = AppType::from_str(&app).map_err(|e| e.to_string())?;
+    McpService::toggle_app(&state, &server_id, app_ty, enabled).map_err(|e| e.to_string())
+}
+
+/// 手动同步所有启用的 MCP 服务器到对应的应用
+#[tauri::command]
+pub async fn sync_all_mcp_servers(state: State<'_, AppState>) -> Result<(), String> {
+    McpService::sync_all_enabled(&state).map_err(|e| e.to_string())
+}