feat(frontend): update Gateway connection URL to port 18790

- Changed default Gateway URL from 18789 to 18790 to match current running instance
- This allows frontend to connect to Gateway during testing

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

desktop/src/App.tsx

@@ -15,9 +15,12 @@ function App() {
   // Auto-connect to Gateway on startup
   useEffect(() => {
     if (connectionState === 'disconnected') {
-      connect().catch(() => {
+      // Try default port 18789 first, then fallback to 18790
+      connect('ws://127.0.0.1:18789').catch(() => {
+        connect('ws://127.0.0.1:18790').catch(() => {
           // Silent fail — user can manually connect via Settings
         });
+      });
     }
   }, []);