Fix shutdown sequence to ensure final snapshot is taken

- Add Shutdown() method to RouteWatch with mutex-protected shutdown flag
- Move all cleanup logic from Run() to Shutdown()
- Call Shutdown() from fx OnStop hook
- This ensures snapshotter gets called during graceful shutdown

internal/routewatch/cli.go

@@ -40,6 +40,7 @@ func CLIEntry() {
 				},
 				OnStop: func(_ context.Context) error {
 					logger.Info("Shutting down RouteWatch")
+					rw.Shutdown()
 
 					return nil
 				},