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

src/config/settings/registry.ts

@@ -459,6 +459,9 @@ function categoryAndSection(path: string): { category: ConfigSettingsCategory; s
   if (path.startsWith('subsync.')) {
     return { category: 'integrations', section: topSection(path) };
   }
+  if (path.startsWith('subtitleSelection.')) {
+    return { category: 'behavior', section: 'Subtitle Selection' };
+  }
   if (path.startsWith('subtitleGeneration.')) {
     return { category: 'integrations', section: 'Japanese Subtitle Generation' };
   }
@@ -635,6 +638,7 @@ function subsectionForPath(path: string): string | undefined {
       leaf === 'openRuntimeOptions' ||
       leaf === 'openJimaku' ||
       leaf === 'openTsukihime' ||
+      leaf === 'openSubtitleSelection' ||
       leaf === 'openSubtitleGeneration' ||
       leaf === 'openSessionHelp' ||
       leaf === 'openControllerSelect' ||