feat: implement product search, media library, and vendor customers

- Add full-text product search in ProductService.search_products()
  searching titles, descriptions, SKUs, brands, and GTINs
- Implement complete vendor media library with file uploads,
  thumbnails, folders, and product associations
- Implement vendor customers API with listing, details, orders,
  statistics, and status management
- Add shop search results UI with pagination and add-to-cart
- Add vendor media library UI with drag-drop upload and grid view
- Add database migration for media_files and product_media tables
- Update TODO file with current launch status (~95% complete)

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

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

app/templates/vendor/partials/sidebar.html

@@ -103,6 +103,7 @@
     {{ section_header('Shop & Content', 'shop', 'color-swatch') }}
     {% call section_content('shop') %}
         {{ menu_item('content-pages', 'content-pages', 'document-text', 'Content Pages') }}
+        {{ menu_item('media', 'media', 'photograph', 'Media Library') }}
         {# Future: Theme customization, if enabled for vendor tier
         {{ menu_item('theme', 'theme', 'paint-brush', 'Theme') }}
         #}