refactor: migrate schemas to canonical module locations

Migrate remaining legacy schemas to their respective modules:

Marketplace module (app/modules/marketplace/schemas/):
- letzshop.py: Letzshop credentials, orders, fulfillment, sync
- onboarding.py: Vendor onboarding wizard schemas

Catalog module (app/modules/catalog/schemas/):
- product.py: ProductCreate, ProductUpdate, ProductResponse

Payments module (app/modules/payments/schemas/):
- payment.py: PaymentConfig, Stripe, transactions, balance

Delete legacy files:
- models/schema/letzshop.py
- models/schema/onboarding.py
- models/schema/product.py
- models/schema/payment.py
- models/schema/marketplace_product.py (re-export)
- models/schema/marketplace_import_job.py (re-export)
- models/schema/search.py (empty)

Update imports across 19 files to use canonical locations.

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

models/schema/__init__.py

@@ -7,6 +7,9 @@ Note: Many schemas have been migrated to their respective modules:
 - Inventory schemas: app.modules.inventory.schemas
 - Message schemas: app.modules.messaging.schemas
 - Cart schemas: app.modules.cart.schemas
+- Marketplace schemas: app.modules.marketplace.schemas
+- Catalog/Product schemas: app.modules.catalog.schemas
+- Payment schemas: app.modules.payments.schemas
 """
 
 # Import API model modules that remain in legacy location
@@ -14,9 +17,6 @@ from . import (
     auth,
     base,
     email,
-    marketplace_import_job,
-    marketplace_product,
-    onboarding,
     vendor,
 )
 
@@ -27,8 +27,5 @@ __all__ = [
     "base",
     "auth",
     "email",
-    "marketplace_product",
-    "onboarding",
     "vendor",
-    "marketplace_import_job",
 ]