[Bug] /api/run/:id returns 404 when server starts after UI

[MyNameIsEdi]

Steps to Reproduce

1. Run npm run dev (starts UI + server concurrently)
2. The browser opens and loads immediately
3. Before the Express server fully initializes, click Run on any agent
4. The request to /api/run/:id returns 404

Expected

The UI should wait for the server to be ready, or show a 'server not ready' state instead of a 404 error.

Suggested Fix

Add a /api/health endpoint and have the UI poll it on startup before enabling Run buttons.