feat: Update API endpoint usage in repositories to remove redundant path property

- Refactored multiple repository implementations across client and staff features to directly use endpoint objects without accessing the `path` property.
- Introduced a new `FeatureGate` class for client-side feature gating based on user scopes, allowing for better access control to API endpoints.
- Added `ApiEndpoint` class to represent API endpoints with their paths and required scopes for future feature gating.

apps/mobile/packages/features/staff/authentication/lib/src/data/repositories_impl/auth_repository_impl.dart

@@ -63,7 +63,7 @@ class AuthRepositoryImpl implements AuthRepositoryInterface {
 
     try {
       final domain.ApiResponse startResponse = await _apiService.post(
-        AuthEndpoints.staffPhoneStart.path,
+        AuthEndpoints.staffPhoneStart,
         data: <String, dynamic>{
           'phoneNumber': phoneNumber,
         },
@@ -182,7 +182,7 @@ class AuthRepositoryImpl implements AuthRepositoryInterface {
     // Step 3: Call V2 verify endpoint with the Firebase ID token.
     final String v2Mode = mode == AuthMode.signup ? 'sign-up' : 'sign-in';
     final domain.ApiResponse response = await _apiService.post(
-      AuthEndpoints.staffPhoneVerify.path,
+      AuthEndpoints.staffPhoneVerify,
       data: <String, dynamic>{
         'idToken': idToken,
         'mode': v2Mode,
@@ -233,7 +233,7 @@ class AuthRepositoryImpl implements AuthRepositoryInterface {
   @override
   Future<void> signOut() async {
     try {
-      await _apiService.post(AuthEndpoints.staffSignOut.path);
+      await _apiService.post(AuthEndpoints.staffSignOut);
     } catch (_) {
       // Sign-out should not fail even if the API call fails.
       // The local sign-out below will clear the session regardless.

apps/mobile/packages/features/staff/authentication/lib/src/data/repositories_impl/profile_setup_repository_impl.dart

@@ -27,7 +27,7 @@ class ProfileSetupRepositoryImpl implements ProfileSetupRepository {
     required List<String> skills,
   }) async {
     final ApiResponse response = await _apiService.post(
-      StaffEndpoints.profileSetup.path,
+      StaffEndpoints.profileSetup,
       data: <String, dynamic>{
         'fullName': fullName,
         if (bio != null && bio.isNotEmpty) 'bio': bio,