Web: lock controls while acquiring; guider telemetry

Guider telemetry: /guider was never polled (it is not in api.ini), so
the guider aside and the Guide button lock never received data.
- new read-only GET /guider/status, polled by a "guider" telemetry loop
- aside keys guider-status-active, guider-status-last_correction-0/1

busy-guard.js greys out and locks the controls of a section while its
acquisition runs, from server telemetry (holds after reload, in other
browsers, and for OBs started by the scheduler):
- scicam section: Expose running -> all but Stop; loop on -> all but
  its loop switch
- teccam section: loop on -> all but its loop switch
- guider (now in its own section): Guide active -> all but Stop
Controls are locked with `inert`, not `disabled`, so the guard does not
interfere with controls disabled for other reasons. GET /sequencer/run
now reports the cam_id the template runs on. Replaces the ad-hoc Expose
and Guide button locks.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>