feat: Implement centralized module management system

- Add ModuleRegistry for managing built-in modules (newsletter, wishlist, affiliate, subscription, licensing)
- Add ModulesController REST API for module enable/disable
- Create Modules settings page with category grouping and toggle controls
- Integrate module checks across admin-spa and customer-spa
- Add useModules hook for both SPAs to check module status
- Hide newsletter from footer builder when module disabled
- Hide wishlist features when module disabled (product cards, account menu, wishlist page)
- Protect wishlist API endpoints with module checks
- Auto-update navigation tree when modules toggled
- Clean up obsolete documentation files
- Add comprehensive documentation:
  - MODULE_SYSTEM_IMPLEMENTATION.md
  - MODULE_INTEGRATION_SUMMARY.md
  - ADDON_MODULE_INTEGRATION.md (proposal)
  - ADDON_MODULE_DESIGN_DECISIONS.md (design doc)
  - FEATURE_ROADMAP.md
  - SHIPPING_INTEGRATION.md

Module system provides:
- Centralized enable/disable for all features
- Automatic navigation updates
- Frontend/backend integration
- Foundation for addon-module unification

customer-spa/src/pages/Account/Wishlist.tsx

@@ -6,6 +6,7 @@ import { useCartStore } from '@/lib/cart/store';
 import { Button } from '@/components/ui/button';
 import { formatPrice } from '@/lib/currency';
 import { toast } from 'sonner';
+import { useModules } from '@/hooks/useModules';
 
 interface WishlistItem {
   product_id: number;
@@ -26,6 +27,32 @@ export default function Wishlist() {
   const { addItem } = useCartStore();
   const [items, setItems] = useState<WishlistItem[]>([]);
   const [loading, setLoading] = useState(true);
+  const { isEnabled, isLoading: modulesLoading } = useModules();
+
+  if (modulesLoading) {
+    return (
+      <div className="min-h-screen flex items-center justify-center">
+        <div className="animate-spin rounded-full h-8 w-8 border-b-2 border-gray-900"></div>
+      </div>
+    );
+  }
+
+  if (!isEnabled('wishlist')) {
+    return (
+      <div className="min-h-screen flex items-center justify-center px-4">
+        <div className="max-w-md w-full bg-yellow-50 border border-yellow-200 rounded-lg p-8 text-center">
+          <Heart className="h-16 w-16 text-yellow-600 mx-auto mb-4" />
+          <h2 className="text-2xl font-bold mb-2">Wishlist Not Available</h2>
+          <p className="text-gray-600 mb-6">
+            The wishlist feature is currently disabled.
+          </p>
+          <Button onClick={() => navigate('/')} className="w-full">
+            Continue Shopping
+          </Button>
+        </div>
+      </div>
+    );
+  }
 
   useEffect(() => {
     loadWishlist();