- Generate a fresh pre-auth key for every agent startup
- Preserve existing tailscale state to avoid creating a new host
- Auto-approve pending auth requests via /api/v1/auth/approve
- Show approval link in settings UI as fallback
Closes HP-558
Apparently I didn't use my brain cells and rely on the /version
endpoint that Headscale has exposed since 0.26 (our lowest supported
version). Switching to that significantly simplifies the API surface.