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/main/runtime/global-shortcuts-runtime-handlers.test.ts

@@ -20,6 +20,7 @@ function createShortcuts(): ConfiguredShortcuts {
     openRuntimeOptions: null,
     openJimaku: null,
     openTsukihime: null,
+    openSubtitleGeneration: null,
     openSessionHelp: null,
     openControllerSelect: null,
     openControllerDebug: null,