frontend: add electron service bootstrap, preload and api client

FE-001: detect and launch the local mactfs-server, expose a narrow preload
bridge (token, service status, directory picker), and add a unified API
client that auto-attaches the Bearer token. Home becomes a bootstrap gate
with a retry entry. Update task board, FE-001 record and FRONTEND_SPEC.

Co-authored-by: Cursor <cursoragent@cursor.com>

mactfsui/app/lib/electron/index.ts

@@ -0,0 +1,10 @@
+export type { MactfsBridge, ServiceHealth, ServiceStatus } from "./types"
+export {
+  getApiBaseUrl,
+  getBridge,
+  getServiceStatus,
+  getToken,
+  isElectron,
+  selectDirectory,
+  startService,
+} from "./bridge"