Add real-time instance status updates in frontend

[depadeto]

Context

Currently the frontend (frontend/src/App.jsx) shows instance status but doesn't poll for updates.

Task

• Add polling (every 5s) to refresh instance status on the function detail page
• Show a status badge that transitions: deploying → running → error
• Add a timestamp showing "deployed 2 minutes ago" using relative time

Files

• frontend/src/App.jsx — main app component
• frontend/src/index.css — styles

Good first issue — React/JavaScript, no backend changes needed (works with demo mode).