- accept nginx installation status and sites-enabled list
- persist nginx fields in server state
- expose nginx data in monitor overview/admin views
- auto-migrate new server_states columns on startup
- Add server_states.plugin_version column
- Keep openclaw_version for remote OpenClaw runtime version
- Expose plugin_version in monitor server view
- Accept and persist plugin_version in heartbeat payloads
Fixes datetime comparison error when last_seen_at from database is
offset-naive (no timezone info) while 'now' is offset-aware (UTC).
This resolves the TypeError: can't subtract offset-naive and
offset-aware datetimes issue in integration tests.