feat(subtitles): add local Japanese subtitle generation

- Generate Japanese SRTs through the overlay modal or launcher
- Support managed whisper.cpp models and optional dialogue detection

src/types/session-bindings.ts

@@ -23,6 +23,7 @@ export type SessionActionId =
   | 'openControllerDebug'
   | 'openJimaku'
   | 'openTsukihime'
+  | 'openSubtitleGeneration'
   | 'openYoutubePicker'
   | 'openPlaylistBrowser'
   | 'replayCurrentSubtitle'