feat: show playlist description in detail view

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

app.js

@@ -439,6 +439,8 @@ async function loadPlaylistDetail(pl){
     const songs=full.entry||[];
     const totalMin=Math.round(songs.reduce((s,t)=>s+(t.duration||0),0)/60);
     document.getElementById('playlist-detail-stats').textContent=`${songs.length} Titel · ${totalMin} Min.`;
+    const descEl=document.getElementById('playlist-detail-desc');
+    if(descEl){descEl.textContent=full.comment||'';descEl.style.display=full.comment?'':'none';}
     document.getElementById('btn-play-playlist').onclick=()=>playQueue(songs,0);
     document.getElementById('btn-shuffle-playlist').onclick=()=>{
       const shuffled=[...songs].sort(()=>Math.random()-.5);