feat(mcp): use project config as SSOT and sync enabled servers to ~/.claude.json

- Add McpConfig to MultiAppConfig and persist MCP servers in ~/.cc-switch/config.json
- Add Tauri commands: get_mcp_config, upsert_mcp_server_in_config, delete_mcp_server_in_config, set_mcp_enabled, sync_enabled_mcp_to_claude, import_mcp_from_claude
- Only write enabled MCPs to ~/.claude.json (mcpServers) and strip UI-only fields (enabled/source)
- Frontend: update API wrappers and MCP panel to read/write via config.json; seed presets on first open; import from ~/.claude.json
- Fix warnings (remove unused mut, dead code)
- Verified with cargo check and pnpm typecheck

src/types.ts

@@ -75,3 +75,9 @@ export interface McpStatus {
   userConfigExists: boolean;
   serverCount: number;
 }
+
+// 新：来自 config.json 的 MCP 列表响应
+export interface McpConfigResponse {
+  configPath: string;
+  servers: Record<string, McpServer>;
+}