feat: explicit metadata, lyrics embedding, E badge in global search

Backend:
- fetchLyrics() queries LRCLIB for plain + synced lyrics
- Synced lyrics saved as .lrc file (Navidrome reads these)
- Plain lyrics embedded via ffmpeg -metadata lyrics=
- ITUNESADVISORY=1 written for explicit tracks
- explicit flag passed through album/track download chain
- fetchItunesTracks + searchItunesAlbumTracks use country=us&explicit=Yes

Frontend:
- explicit:true sent in download payload from iTunes track data
- "E" badge shown on explicit tracks in global search track list

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

src/views.js

@@ -128,7 +128,7 @@ export function makeGlobalTrackItem(t, idx, list) {
   el.innerHTML = `
     <div class="gtrack-art">${art ? `<img src="${art}" loading="lazy">` : '<div style="width:100%;height:100%;display:flex;align-items:center;justify-content:center;font-size:22px">🎵</div>'}</div>
     <div class="gtrack-info">
-      <div class="gtrack-title">${esc(t.trackName||t.collectionName||'—')}</div>
+      <div class="gtrack-title">${esc(t.trackName||t.collectionName||'—')}${t.trackExplicitness==='explicit'?'<span class="explicit-badge">E</span>':''}</div>
       <div class="gtrack-sub">${esc(t.artistName||'—')} · ${esc(t.collectionName||'')} ${t.releaseDate?'· '+new Date(t.releaseDate).getFullYear():''}</div>
     </div>
     <div class="gtrack-actions">