feat(overlay): add optional subtitle selection modal (#265)

src/config/definitions/template-sections.ts

@@ -1,6 +1,12 @@
 import { ConfigTemplateSection } from './shared';
 
 const CORE_TEMPLATE_SECTIONS: ConfigTemplateSection[] = [
+  {
+    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: [