Add TenantCustomTier system and fix BusinessEditModal feature loading

Backend:
- Add TenantCustomTier model for per-tenant feature overrides
- Update EntitlementService to check custom tier before plan features
- Add custom_tier action on TenantViewSet (GET/PUT/DELETE)
- Add Celery task for grace period management (30-day expiry)

Frontend:
- Add DynamicFeaturesEditor component for dynamic feature management
- Fix BusinessEditModal to load features from plan defaults when no custom tier
- Update limits (max_users, max_resources, etc.) to use featureValues
- Remove outdated canonical feature check from FeaturePicker (removes warning icons)
- Add useBillingPlans hook for accessing billing system data
- Add custom tier API functions to platform.ts

Features now follow consistent rules:
- Load from plan defaults when no custom tier exists
- Load from custom tier when one exists
- Reset to plan defaults when plan changes
- Save to custom tier on edit

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/App.tsx

@@ -114,6 +114,7 @@ const ContractSigning = React.lazy(() => import('./pages/ContractSigning')); //
 const PageEditor = React.lazy(() => import('./pages/PageEditor')); // Import PageEditor
 const PublicPage = React.lazy(() => import('./pages/PublicPage')); // Import PublicPage
 const BookingFlow = React.lazy(() => import('./pages/BookingFlow')); // Import Booking Flow
+const Locations = React.lazy(() => import('./pages/Locations')); // Import Locations management page
 
 // Settings pages
 const SettingsLayout = React.lazy(() => import('./layouts/SettingsLayout'));
@@ -832,6 +833,16 @@ const AppContent: React.FC = () => {
                 )
               }
             />
+            <Route
+              path="/locations"
+              element={
+                hasAccess(['owner', 'manager']) ? (
+                  <Locations />
+                ) : (
+                  <Navigate to="/" />
+                )
+              }
+            />
             <Route
               path="/my-availability"
               element={