fix: auto-restart — Vite dev server keeps dying

[kagura-agent]

Problem

Vite dev server (port 5173) has crashed multiple times during development. Luna has to report it before we notice.

Solution

Options:

1. Use pm2 or a simple bash loop for process supervision
2. Add health check to heartbeat
3. Long-term: serve built frontend from the server process (no separate Vite)

Acceptance Criteria

• Frontend stays up reliably
• Crash is detected and recovered automatically