refactor: switch to full auto-discovery for module API routes

- Enhanced route discovery system with ROUTE_CONFIG support for custom
  prefix, tags, and priority
- Added get_admin_api_routes() and get_vendor_api_routes() helpers that
  return routes sorted by priority
- Added fallback discovery for routes/{frontend}.py when routes/api/
  doesn't exist
- Updated CMS module with ROUTE_CONFIG (prefix: /content-pages,
  priority: 100) to register last for catch-all routes
- Moved customers routes from routes/ to routes/api/ directory
- Updated orders module to aggregate exception routers into main routers
- Removed manual module router imports from admin and vendor API init
  files, replaced with auto-discovery loop

Modules now auto-discovered: billing, inventory, orders, marketplace,
cms, customers, analytics, loyalty, messaging, monitoring, dev-tools

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

app/modules/customers/routes/api/__init__.py

@@ -6,4 +6,20 @@ from app.modules.customers.routes.api.storefront import router as storefront_rou
 # Tag for OpenAPI documentation
 STOREFRONT_TAG = "Customer Account (Storefront)"
 
-__all__ = ["storefront_router", "STOREFRONT_TAG"]
+__all__ = [
+    "storefront_router",
+    "STOREFRONT_TAG",
+    "admin_router",
+    "vendor_router",
+]
+
+
+def __getattr__(name: str):
+    """Lazy import routers to avoid circular dependencies."""
+    if name == "admin_router":
+        from app.modules.customers.routes.api.admin import admin_router
+        return admin_router
+    elif name == "vendor_router":
+        from app.modules.customers.routes.api.vendor import vendor_router
+        return vendor_router
+    raise AttributeError(f"module {__name__!r} has no attribute {name!r}")