0.0.24

Self-healing watcher watchdog + hard-exit on lost instance lock

Heartbeat logs revealed the recurring "no buttons" state: after an
update one process's poll loop had died while a second post-update
process never started its watcher (lost the lock, lingered as a zombie).

- Watchdog: an independent interval restarts the poll loop if it goes
  quiet, so detection self-heals from ANY stall without a manual relaunch.
- A second instance now app.exit(0)s immediately instead of the async
  app.quit(), so it can't linger as a watcher-less zombie owning the tray.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>