feat: synced lyrics view in Now Playing overlay

Adds a Lyrics tab to the NP overlay using Navidrome's getLyricsBySongId
endpoint. Synced lyrics auto-scroll and highlight the current line as
the track plays; tapping a line seeks to that position. Falls back to
plain text for unsynced lyrics.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/api.js

@@ -16,6 +16,12 @@ export async function api(method, extra='') {
   return r;
 }
 export function streamUrl(id) { return apiUrl('stream', `&id=${id}&format=raw`); }
+export async function getLyricsBySongId(songId) {
+  try {
+    const r = await api('getLyricsBySongId', `&id=${songId}`);
+    return r.lyricsList?.structuredLyrics ?? [];
+  } catch { return []; }
+}
 export function downloadUrl(id) { return apiUrl('download', `&id=${id}`); }
 export function coverUrl(id, size=300) { return id ? apiUrl('getCoverArt', `&id=${id}&size=${size}`) : null; }