refactor(customers): remove legacy route files, fully self-contained

- Delete app/api/v1/admin/customers.py (no backward compatibility)
- Delete app/api/v1/vendor/customers.py (no backward compatibility)
- Remove legacy router aliases from module routes
- Routes now fully self-contained in app/modules/customers/routes/

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

app/api/v1/admin/customers.py

@@ -1,31 +0,0 @@
-# app/api/v1/admin/customers.py
-"""
-LEGACY LOCATION - Re-exports from module for backwards compatibility.
-
-The canonical implementation is now in:
-    app/modules/customers/routes/admin.py
-
-This file exists to maintain backwards compatibility with code that
-imports from the old location. All new code should import directly
-from the module:
-
-    from app.modules.customers.routes.admin import admin_router
-"""
-
-from app.modules.customers.routes.admin import (
-    admin_router,
-    router,
-    list_customers,
-    get_customer_stats,
-    get_customer,
-    toggle_customer_status,
-)
-
-__all__ = [
-    "admin_router",
-    "router",
-    "list_customers",
-    "get_customer_stats",
-    "get_customer",
-    "toggle_customer_status",
-]