fix: better session management for github_copilot_provider

cmd/picoclaw/cmd_gateway.go

@@ -212,6 +212,9 @@ func gatewayCmd() {
 
 	fmt.Println("\nShutting down...")
 	cancel()
+	if cp, ok := provider.(providers.SessionProvider); ok {
+		cp.Close()
+	}
 	healthServer.Stop(context.Background())
 	deviceService.Stop()
 	heartbeatService.Stop()