feat: add media library picker for product images

- Add admin media API endpoints for vendor media management
- Create reusable media_picker_modal macro in modals.html
- Create mediaPickerMixin Alpine.js helper for media selection
- Update product create/edit forms with media picker UI
- Support main image + additional images selection
- Add upload functionality within the picker modal
- Update vendor_product_service to handle additional_images
- Add additional_images field to Pydantic schemas

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

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

app/api/v1/admin/__init__.py

@@ -40,6 +40,7 @@ from . import (
     letzshop,
     logs,
     marketplace,
+    media,
     messages,
     monitoring,
     notifications,
@@ -173,6 +174,9 @@ router.include_router(logs.router, tags=["admin-logs"])
 # Include image management endpoints
 router.include_router(images.router, tags=["admin-images"])
 
+# Include media library management endpoints
+router.include_router(media.router, tags=["admin-media"])
+
 # Include platform health endpoints
 router.include_router(
     platform_health.router, prefix="/platform", tags=["admin-platform-health"]