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/definitions/defaults-core.ts

@@ -103,6 +103,7 @@ export const CORE_DEFAULT_CONFIG: Pick<
     openRuntimeOptions: 'CommandOrControl+Shift+O',
     openJimaku: 'Ctrl+Shift+J',
     openTsukihime: 'Ctrl+Shift+T',
+    openSubtitleSelection: 'g-s',
     openSubtitleGeneration: 'Ctrl+Shift+G',
     openSessionHelp: 'CommandOrControl+Slash',
     openControllerSelect: 'Alt+C',

src/config/definitions/options-core.ts

@@ -642,6 +642,13 @@ export function buildCoreConfigOptionRegistry(
       defaultValue: defaultConfig.shortcuts.openSessionHelp,
       description: 'Accelerator that opens the session help / keybinding cheatsheet.',
     },
+    {
+      path: 'shortcuts.openSubtitleSelection',
+      kind: 'string',
+      defaultValue: defaultConfig.shortcuts.openSubtitleSelection,
+      description:
+        'Open subtitle selection when enabled. Use g-s to press g then s. Set null to unbind.',
+    },
     {
       path: 'shortcuts.openSubtitleGeneration',
       kind: 'string',

src/config/definitions/options-subtitle.ts

@@ -6,6 +6,13 @@ export function buildSubtitleConfigOptionRegistry(
   defaultConfig: ResolvedConfig,
 ): ConfigOptionRegistryEntry[] {
   return [
+    {
+      path: 'subtitleSelection.enabled',
+      kind: 'boolean',
+      defaultValue: defaultConfig.subtitleSelection.enabled,
+      description:
+        'Use the SubMiner modal to select primary and secondary subtitle tracks. When enabled, its shortcut overrides mpv subtitle selection.',
+    },
     ...(
       ['whisperPath', 'modelPath', 'ffmpegPath', 'ffprobePath', 'vadModelPath', 'vadPath'] as const
     ).map((key) => ({

src/config/definitions/template-sections.ts

@@ -17,6 +17,12 @@ const CORE_TEMPLATE_SECTIONS: ConfigTemplateSection[] = [
     notes: ['Used only while Hachidori is linked to an external host.'],
     key: 'hachidori',
   },
+  {
+    title: 'Subtitle Selection',
+    description: ['Select primary and secondary mpv subtitle tracks from the overlay.'],
+    notes: ['Hot-reload: enabling or disabling updates the session shortcut immediately.'],
+    key: 'subtitleSelection',
+  },
   {
     title: 'Japanese Subtitle Generation',
     description: [