feat(desktop): wire MCP client to settings UI

- MCPServices.tsx now calls real Tauri commands (start/stop/list)
  instead of only toggling config flags
- Show running service count, discovered tools per service
- Expand/collapse tool list for each running MCP service
- Extended QuickConfig mcpServices type with command/args/env/cwd
- Config change persists enabled state, MCP start/stop happens live

desktop/src/store/configStore.ts

@@ -23,7 +23,15 @@ export interface QuickConfig {
   gatewayUrl?: string;
   gatewayToken?: string;
   skillsExtraDirs?: string[];
-  mcpServices?: Array<{ id: string; name: string; enabled: boolean }>;
+  mcpServices?: Array<{
+    id: string;
+    name: string;
+    enabled: boolean;
+    command?: string;
+    args?: string[];
+    env?: Record<string, string>;
+    cwd?: string;
+  }>;
   theme?: 'light' | 'dark';
   autoStart?: boolean;
   showToolCalls?: boolean;