* feat(recognition): cancel in-progress transcription with hotkey
Adds per-session cancellation across the manager, tray, and Test Dictation.
Fixes#991
* fix(settings): keep Test Dictation cancellation responsive
Fixes#991
* fix(recognition): keep late workers cancellable (#991)
* test(tray): avoid early tray import in cancellation tests
* fix(recognition): keep a cancelled capture thread out of the next session
A cancel returns to IDLE without joining the capture thread, so a thread
still in its reconnection backoff could wake inside a newer recording,
reopen that session's device and write into its buffer. Tie the capture
loop and the reconnection to the session's cancel token: a cancelled or
replaced session stops reading, skips the reopen and exits without
raising an error.
