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/components/ProductCard.tsx

@@ -6,6 +6,7 @@ import { Button } from './ui/button';
 import { useLayout } from '@/contexts/ThemeContext';
 import { useShopSettings } from '@/hooks/useAppearanceSettings';
 import { useWishlist } from '@/hooks/useWishlist';
+import { useModules } from '@/hooks/useModules';
 
 interface ProductCardProps {
   product: {
@@ -28,8 +29,10 @@ export function ProductCard({ product, onAddToCart }: ProductCardProps) {
   const { isClassic, isModern, isBoutique, isLaunch } = useLayout();
   const { layout, elements, addToCart, saleBadge, isLoading } = useShopSettings();
   const { isEnabled: wishlistEnabled, isInWishlist, toggleWishlist } = useWishlist();
+  const { isEnabled: isModuleEnabled } = useModules();
   
-  const inWishlist = wishlistEnabled && isInWishlist(product.id);
+  const showWishlist = isModuleEnabled('wishlist') && wishlistEnabled;
+  const inWishlist = showWishlist && isInWishlist(product.id);
   
   const handleWishlistClick = async (e: React.MouseEvent) => {
     e.preventDefault();
@@ -142,7 +145,7 @@ export function ProductCard({ product, onAddToCart }: ProductCardProps) {
             )}
             
             {/* Wishlist Button */}
-            {wishlistEnabled && (
+            {showWishlist && (
               <div className="absolute top-2 left-2 z-10">
                 <button 
                   onClick={handleWishlistClick}
@@ -246,7 +249,7 @@ export function ProductCard({ product, onAddToCart }: ProductCardProps) {
             )}
             
             {/* Wishlist Button */}
-            {wishlistEnabled && (
+            {showWishlist && (
               <div className="absolute top-4 right-4 z-10">
                 <button 
                   onClick={handleWishlistClick}
@@ -366,7 +369,7 @@ export function ProductCard({ product, onAddToCart }: ProductCardProps) {
             )}
             
             {/* Wishlist Button */}
-            {wishlistEnabled && (
+            {showWishlist && (
               <div className="absolute top-6 left-6 z-10">
                 <button 
                   onClick={handleWishlistClick}
@@ -440,7 +443,7 @@ export function ProductCard({ product, onAddToCart }: ProductCardProps) {
           )}
           
           {/* Wishlist Button */}
-          {wishlistEnabled && (
+          {showWishlist && (
             <div className="absolute top-3 right-3 z-10">
               <button 
                 onClick={handleWishlistClick}