refactor: fix architecture violations with provider patterns and dependency inversion

Major changes:
- Add AuditProvider protocol for cross-module audit logging
- Move customer order operations to orders module (dependency inversion)
- Add customer order metrics via MetricsProvider pattern
- Fix missing db parameter in get_admin_context() calls
- Move ProductMedia relationship to catalog module (proper ownership)
- Add marketplace breakdown stats to marketplace_widgets

New files:
- contracts/audit.py - AuditProviderProtocol
- core/services/audit_aggregator.py - Aggregates audit providers
- monitoring/services/audit_provider.py - Monitoring audit implementation
- orders/services/customer_order_service.py - Customer order operations
- orders/routes/api/vendor_customer_orders.py - Customer order endpoints
- catalog/services/product_media_service.py - Product media service
- Architecture documentation for patterns

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

app/modules/cms/models/__init__.py

@@ -4,14 +4,15 @@ CMS module database models.
 
 This is the canonical location for CMS models including:
 - ContentPage: CMS pages (marketing, vendor default pages)
-- MediaFile: Vendor media library
+- MediaFile: Vendor media library (generic, consumer-agnostic)
 - VendorTheme: Vendor storefront theme configuration
 
 Usage:
     from app.modules.cms.models import ContentPage, MediaFile, VendorTheme
 
-For product-media associations:
-    from app.modules.catalog.models import ProductMedia
+Note: ProductMedia is in the catalog module since it's catalog's association
+to media files. CMS provides generic media storage, consumers define their
+own associations.
 """
 
 from app.modules.cms.models.content_page import ContentPage