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- Remove outdated canonical feature check from FeaturePicker (removes warning icons)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/pages/PluginMarketplace.tsx

@@ -98,7 +98,7 @@ const PluginMarketplace: React.FC = () => {
   const hasPluginsFeature = canUse('plugins');
   const isLocked = !hasPluginsFeature;
 
-  // Fetch marketplace plugins
+  // Fetch marketplace plugins - only when user has the feature
   const { data: plugins = [], isLoading, error } = useQuery<PluginTemplate[]>({
     queryKey: ['plugin-templates', 'marketplace'],
     queryFn: async () => {
@@ -121,6 +121,8 @@ const PluginMarketplace: React.FC = () => {
         pluginCode: p.plugin_code,
       }));
     },
+    // Don't fetch if user doesn't have the plugins feature
+    enabled: hasPluginsFeature && !permissionsLoading,
   });
 
   // Fetch installed plugins to check which are already installed
@@ -130,6 +132,8 @@ const PluginMarketplace: React.FC = () => {
       const { data } = await api.get('/plugin-installations/');
       return data;
     },
+    // Don't fetch if user doesn't have the plugins feature
+    enabled: hasPluginsFeature && !permissionsLoading,
   });
 
   // Create a set of installed template IDs for quick lookup
@@ -223,7 +227,10 @@ const PluginMarketplace: React.FC = () => {
     );
   }
 
-  if (error) {
+  // Check if error is a 403 (plan restriction) - show upgrade prompt instead
+  const is403Error = error && (error as any)?.response?.status === 403;
+
+  if (error && !is403Error) {
     return (
       <div className="p-8">
         <div className="bg-red-50 dark:bg-red-900/20 border border-red-200 dark:border-red-800 rounded-lg p-4">
@@ -235,8 +242,11 @@ const PluginMarketplace: React.FC = () => {
     );
   }
 
+  // If 403 error, treat as locked
+  const effectivelyLocked = isLocked || is403Error;
+
   return (
-    <LockedSection feature="plugins" isLocked={isLocked} variant="overlay">
+    <LockedSection feature="plugins" isLocked={effectivelyLocked} variant="overlay">
     <div className="p-8 space-y-6 max-w-7xl mx-auto">
       {/* Header */}
       <div className="flex items-center justify-between">