- Move U+FFFC placeholder detection before _record_last_inbound() so the
placeholder message id is not recorded as the reaction target
- Cancel pending U+FFFC tasks in disconnect() to prevent task leaks
- Check mimeType audio/x-caf in addition to filename for CAF→VOICE promotion,
fixing unnamed attachments that default to '(unnamed)'
- Add 7 Photon adapter tests: CAF named/unnamed promotion, U+FFFC no-dispatch,
U+FFFC not recorded as last inbound, U+FFFC+attachment cancel, timeout fire,
disconnect cleanup
- Add 6 transcription tests: ffmpeg conversion, afconvert fallback, all-fail,
CAF→WAV before Groq, conversion failure error, local provider skip
afab7ed46e