fix: align youtube playback with shared overlay startup

src/core/services/youtube/labels.ts

@@ -0,0 +1,40 @@
+export type YoutubeTrackKind = 'manual' | 'auto';
+
+export function normalizeYoutubeLangCode(value: string): string {
+  return value.trim().toLowerCase().replace(/_/g, '-').replace(/[^a-z0-9-]+/g, '');
+}
+
+export function isJapaneseYoutubeLang(value: string): boolean {
+  const normalized = normalizeYoutubeLangCode(value);
+  return (
+    normalized === 'ja' ||
+    normalized === 'jp' ||
+    normalized === 'jpn' ||
+    normalized === 'japanese' ||
+    normalized.startsWith('ja-') ||
+    normalized.startsWith('jp-')
+  );
+}
+
+export function isEnglishYoutubeLang(value: string): boolean {
+  const normalized = normalizeYoutubeLangCode(value);
+  return (
+    normalized === 'en' ||
+    normalized === 'eng' ||
+    normalized === 'english' ||
+    normalized === 'enus' ||
+    normalized === 'en-us' ||
+    normalized.startsWith('en-')
+  );
+}
+
+export function formatYoutubeTrackLabel(input: {
+  language: string;
+  kind: YoutubeTrackKind;
+  title?: string;
+}): string {
+  const language = input.language.trim() || 'unknown';
+  const base = input.title?.trim() || language;
+  return `${base} (${input.kind})`;
+}
+