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/availability/lib/src/data/repositories_impl/availability_repository_impl.dart

@@ -25,7 +25,7 @@ class AvailabilityRepositoryImpl implements AvailabilityRepository {
     final String endDate = _toIsoDate(end);
 
     final ApiResponse response = await _apiService.get(
-      StaffEndpoints.availability.path,
+      StaffEndpoints.availability,
       params: <String, dynamic>{
         'startDate': startDate,
         'endDate': endDate,
@@ -48,7 +48,7 @@ class AvailabilityRepositoryImpl implements AvailabilityRepository {
     required List<TimeSlot> slots,
   }) async {
     final ApiResponse response = await _apiService.put(
-      StaffEndpoints.availability.path,
+      StaffEndpoints.availability,
       data: <String, dynamic>{
         'dayOfWeek': dayOfWeek,
         'availabilityStatus': status.toJson(),
@@ -86,7 +86,7 @@ class AvailabilityRepositoryImpl implements AvailabilityRepository {
     }
 
     await _apiService.post(
-      StaffEndpoints.availabilityQuickSet.path,
+      StaffEndpoints.availabilityQuickSet,
       data: data,
     );
   }