Ensure subscription router is always mounted without duplicates

backend/app.py

@@ -260,6 +260,9 @@ async def onboarding_status():
 
 # Include routers using modular utilities
 router_manager.include_core_routers()
+# Safety net: keep subscription routes available even if core inclusion flow changes
+# in special modes (e.g., demo mode). De-dup is handled by RouterManager.
+router_manager.include_router_safely(subscription_router, "subscription")
 router_manager.include_optional_routers()
 
 # Include assets serving router (must be mounted to serve generated images)