Implements REST API endpoints to enable automatic registration of
temperature proxies during sensor-proxy installation.
API endpoints:
- POST /api/temperature-proxy/register
- Accepts: hostname, proxy_url
- Returns: authentication token
- Finds matching PVE instance and configures proxy URL/token
- No authentication required (called during installation)
- DELETE /api/temperature-proxy/unregister?hostname=X
- Removes proxy configuration from PVE instance
- Requires admin authentication
Implementation:
- Uses config.ConfigPersistence for loading/saving nodes.enc
- Matches PVE instances by hostname in Host field or ClusterEndpoints
- Generates cryptographically secure random tokens (32 bytes, base64)
- Atomic config updates (load → modify → save)
Next step: Update install-sensor-proxy.sh to call registration API
Related to #571
