Implement `subminer stats -b` to start a background stats daemon and
`subminer stats -s` to stop it, with PID-based process lifecycle
management, single-instance lock bypass for daemon mode, and automatic
reuse of running daemon instances.
- POST /api/stats/mine-card endpoint with mode=word|sentence|audio
- mode=word: creates full Yomitan card (definition/reading/pitch) via hidden search page bridge
- mode=sentence/audio: creates card directly with Lapis/Kiku flags
- Audio + image generated in parallel from source video via ffmpeg
- Respects all AnkiConnect config (AVIF, static, field mappings, metadata pattern)
- addYomitanNoteViaSearch calls window.__subminerAddNote exposed by Yomitan fork
- Syncs AnkiConnect URL to Yomitan before each word mine