feat(overlay): add subtitle selection modal and Jellyfin 12 fixes

- Add an optional subtitle selection modal for primary/secondary mpv tracks (subtitleSelection.enabled, g-s sequence shortcut) with key-sequence conflict handling
- Authenticate Jellyfin URLs with the ApiKey query, answer remote keep-alives, clear now-playing on stop, and restore episode titles in Anki misc info
- Honor the configured mpv executable when Jellyfin starts playback via a shared mpv-process launcher
- Bump electron-builder to 26.16.1
- Condense and reconcile changelog fragments; update config example and docs

docs/architecture/README.md

@@ -35,6 +35,8 @@ Update checks and startup launcher migration share a serialized update-state sto
 - `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.
 - 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.
+- `src/shared/session-key-sequences.ts` rejects sequence prefixes reserved by single-key actions. The session-binding compiler reserves configured and built-in overlay keys; `src/main/runtime/session-bindings-runtime.ts` adds active mpv bindings and publishes the effective list to both the plugin artifact and the renderer through `session-bindings:changed`. mpv no-op `ignore` bindings do not reserve prefixes.
 - `src/renderer/` owns overlay rendering and input behavior.
 - `src/config/` owns config definitions, defaults, loading, and resolution.
 - `src/types/` owns shared cross-runtime contracts via domain entrypoints; `src/types.ts` stays a compatibility barrel.

docs/architecture/domains.md

@@ -21,6 +21,7 @@ Read when: you need to find the owner module for a behavior or test surface
   `src/config/resolve/anki-connect/`
 - Overlay/window state: `src/core/services/overlay-*`, `src/main/overlay-*.ts`
 - MPV runtime and protocol: `src/core/services/mpv*.ts`
+  Windows executable lookup and detached process creation are shared in `src/main/runtime/mpv-process.ts`. The Windows launcher and Jellyfin handlers retain their own playback and connection workflows.
 - Subtitle/token pipeline: `src/core/services/subtitle-*.ts`, `src/core/services/tokenizer*`, `src/core/services/tokenizer/`, `src/subsync/`
 - Anki workflow: `src/anki-integration/`, `src/core/services/anki-jimaku*.ts`
 - Immersion tracking: `src/core/services/immersion-tracker/`