Fix UI freeze when camera disconnects during liveview (v0.6.4)

Powering off the camera mid-liveview fired the WebUSB `disconnect`
event, but nothing stopped PTPDevice's internal loops, so they kept
hammering the dead device and froze the renderer:

- PTPDevice#listenDisconnect now marks the device closed and clears the
  command queue on disconnect.
- PTPDevice#listenInterruptIn returns instead of throwing when the
  device is gone, and only reschedules itself while still open.
- TethrSigma#updateLiveviewFrame detaches itself from the queue `idle`
  event once the device is closed, and swallows per-frame fetch errors
  so a disconnect can't surface as an unhandled rejection.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

0.2.0

0.1.0