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/architecture/README.md

@@ -32,7 +32,7 @@ Update checks and startup launcher migration share a serialized update-state sto
 - `src/main/boot/` owns boot-phase assembly seams so `src/main.ts` can stay focused on lifecycle coordination and startup-path selection.
 - `src/main/runtime/linux-overlay-mode-runtime.ts` owns Linux fullscreen mode state and window replacement. App cleanup cancels pending replacements; `main.ts` supplies window creation and subtitle refresh hooks.
 - `src/core/services/` owns focused runtime services plus pure or side-effect-bounded logic.
-- `src/core/services/subtitle-generation*.ts` shares local whisper.cpp transcription, safe model downloads, and progress between the launcher and Electron. Optional dialogue mode retains both Silero-detected speech and other audible sections, omits confidently silent gaps, decodes passages independently, and restores original media timing. `src/main/runtime/subtitle-generation-runtime.ts` owns the overlay job lifecycle and only loads completed subtitles into the same local media; `src/shared/subtitle-generation*.ts` owns configuration, the multilingual model catalog, and IPC contracts. The overlay runtime retains a session model selection, validates picker requests through IPC, and keeps external model paths authoritative.
+- `src/core/services/subtitle-generation*.ts` shares local whisper.cpp transcription, safe model downloads, and progress between the launcher and Electron. Optional dialogue mode retains both Silero-detected speech and other audible sections, omits confidently silent gaps, decodes passages independently, and restores original media timing. `src/main/runtime/subtitle-generation-runtime.ts` owns the overlay job lifecycle and only loads completed subtitles into the same media. For Jellyfin playback it reads the item's original-file stream (`toJellyfinOriginalStreamUrl`) into one reused output folder, where each run best-effort deletes earlier files and writes a uniquely named SRT; transcoded playback uses Jellyfin's audio index and only external references, since mpv's track indexes describe the transcode. Subprocess errors redact URL tokens; `src/shared/subtitle-generation*.ts` owns configuration, the multilingual model catalog, and IPC contracts. The overlay runtime retains a session model selection, validates picker requests through IPC, and keeps external model paths authoritative.
 - Subtitle model recommendations use bounded `nvidia-smi` and Whisper CUDA discovery probes in `subtitle-generation-acceleration.ts`. The overlay runtime caches results by executable path for 30 seconds and exposes acceleration status through the existing status IPC. Recommendations do not alter model selection or transcription arguments.
 - `subtitle-generation-reference.ts` ranks mpv's loaded text subtitle tracks, excludes signs/songs and forced references, and extracts timing hints with FFmpeg. The overlay and launcher snapshot references only for matching media, including active subtitle delays. Hints guide long-passage cuts with or without VAD; they never limit audio coverage or replace Whisper timestamps.
 - `src/main/runtime/subtitle-selection.ts` reads and validates mpv subtitle tracks and applies primary/secondary selections. Its opt-in session shortcut opens the shared overlay modal window, with renderer focus and subtitle suppression handled by the modal registry.