feat: complete marketplace module self-containment

Migrate marketplace module to self-contained structure:

- routes/api/admin.py - Admin API endpoints
- routes/api/vendor.py - Vendor API endpoints
- routes/pages/ - Page routes (placeholder)
- models/letzshop.py - Letzshop model
- models/marketplace_import_job.py - Import job model
- models/marketplace_product.py - Product model
- models/marketplace_product_translation.py - Translation model
- schemas/marketplace_import_job.py - Import job schemas
- schemas/marketplace_product.py - Product schemas
- locales/ - Translations (en, de, fr, lu)

Removed legacy route files replaced by api/ structure.
Updated __init__.py files to use new structure.

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

app/modules/marketplace/__init__.py

@@ -27,12 +27,21 @@ Usage:
     from app.modules.marketplace.exceptions import LetzshopClientError
 """
 
-from app.modules.marketplace.definition import (
-    marketplace_module,
-    get_marketplace_module_with_routers,
-)
+# Lazy imports to avoid circular dependencies
+# Routers and module definition are imported on-demand
 
 __all__ = [
     "marketplace_module",
     "get_marketplace_module_with_routers",
 ]
+
+
+def __getattr__(name: str):
+    """Lazy import to avoid circular dependencies."""
+    if name == "marketplace_module":
+        from app.modules.marketplace.definition import marketplace_module
+        return marketplace_module
+    elif name == "get_marketplace_module_with_routers":
+        from app.modules.marketplace.definition import get_marketplace_module_with_routers
+        return get_marketplace_module_with_routers
+    raise AttributeError(f"module {__name__!r} has no attribute {name!r}")