feat(subtitles): generate Japanese subtitles during Jellyfin playback (#294)

* feat(subtitles): generate Japanese subtitles during Jellyfin playback

- Read the item's original file via toJellyfinOriginalStreamUrl and write output to a temp dir
- Transcoded playback uses Jellyfin's audio index and only external references
- Show Jellyfin media by title and redact URL tokens in subprocess errors
- Update overlay copy, docs, and changelog fragment

* fix(subtitles): redact full stream tokens and reuse one Jellyfin output folder

* test(subtitles): make Jellyfin output path assertions platform-neutral

- Compare dirname/basename via node:path instead of POSIX-only regexes
- Assert the full sub-add command uses the generated output path

docs-site/jellyfin-integration.md

@@ -23,6 +23,8 @@ SubMiner starts mpv if it is not already running. Pause, seek, stop, and track c
 
 SubMiner selects a Japanese subtitle track automatically and resets mpv's subtitle delay to zero. It direct-plays files when it can and asks Jellyfin to transcode the rest.
 
+If an episode has no Japanese subtitles, you can [generate them with Whisper](/subtitle-generation#generating-from-the-overlay) while it plays.
+
 On Windows, casting finds mpv through `mpv.executablePath`, then `SUBMINER_MPV_PATH`, then `PATH`. An invalid `mpv.executablePath` stops mpv from starting.
 
 ## Playing from the terminal