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/client/authentication/lib/src/data/repositories_impl/auth_repository_impl.dart

@@ -45,7 +45,7 @@ class AuthRepositoryImpl implements AuthRepositoryInterface {
       // Step 1: Call V2 sign-in endpoint — server handles Firebase Auth
       // via Identity Toolkit and returns a full auth envelope.
       final ApiResponse response = await _apiService.post(
-        AuthEndpoints.clientSignIn.path,
+        AuthEndpoints.clientSignIn,
         data: <String, dynamic>{
           'email': email,
           'password': password,
@@ -107,7 +107,7 @@ class AuthRepositoryImpl implements AuthRepositoryInterface {
       //   - Creates user, tenant, business, memberships in one transaction
       //   - Returns full auth envelope with session tokens
       final ApiResponse response = await _apiService.post(
-        AuthEndpoints.clientSignUp.path,
+        AuthEndpoints.clientSignUp,
         data: <String, dynamic>{
           'companyName': companyName,
           'email': email,
@@ -172,7 +172,7 @@ class AuthRepositoryImpl implements AuthRepositoryInterface {
   Future<void> signOut() async {
     try {
       // Step 1: Call V2 sign-out endpoint for server-side token revocation.
-      await _apiService.post(AuthEndpoints.clientSignOut.path);
+      await _apiService.post(AuthEndpoints.clientSignOut);
     } catch (e) {
       developer.log(
         'V2 sign-out request failed: $e',