feat: add marketplace products admin UI with copy-to-vendor functionality

- Add admin marketplace products page to browse imported products
- Add admin vendor products page to manage vendor catalog
- Add product detail pages for both marketplace and vendor products
- Implement copy-to-vendor API to copy marketplace products to vendor catalogs
- Add vendor product service with CRUD operations
- Update sidebar navigation with new product management links
- Add integration and unit tests for new endpoints and services

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

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

static/admin/js/marketplace.js

@@ -24,6 +24,9 @@ function adminMarketplace() {
         error: '',
         successMessage: '',
 
+        // Active import tab (marketplace selector)
+        activeImportTab: 'letzshop',
+
         // Vendors list
         vendors: [],
         selectedVendor: null,
@@ -289,6 +292,29 @@ function adminMarketplace() {
             }
         },
 
+        /**
+         * Switch marketplace tab and update form accordingly
+         */
+        switchMarketplace(marketplace) {
+            this.activeImportTab = marketplace;
+
+            // Update marketplace in form
+            const marketplaceMap = {
+                'letzshop': 'Letzshop',
+                'codeswholesale': 'CodesWholesale'
+            };
+            this.importForm.marketplace = marketplaceMap[marketplace] || 'Letzshop';
+
+            // Reset form fields when switching tabs
+            this.importForm.vendor_id = '';
+            this.importForm.csv_url = '';
+            this.importForm.language = 'fr';
+            this.importForm.batch_size = 1000;
+            this.selectedVendor = null;
+
+            adminMarketplaceLog.info('Switched to marketplace:', this.importForm.marketplace);
+        },
+
         /**
          * Quick fill form with saved CSV URL from vendor settings
          */