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/contracts/__init__.py

@@ -45,6 +45,10 @@ Widget Provider Pattern:
             return [DashboardWidget(key="orders.recent", widget_type="list", ...)]
 """
 
+from app.modules.contracts.audit import (
+    AuditEvent,
+    AuditProviderProtocol,
+)
 from app.modules.contracts.base import ServiceProtocol
 from app.modules.contracts.cms import ContentServiceProtocol
 from app.modules.contracts.metrics import (
@@ -67,6 +71,9 @@ __all__ = [
     "ServiceProtocol",
     # CMS protocols
     "ContentServiceProtocol",
+    # Audit protocols
+    "AuditEvent",
+    "AuditProviderProtocol",
     # Metrics protocols
     "MetricValue",
     "MetricsContext",