feat(playlists): show playlist cover in the "add to playlist" picker (web + Android)

The picker listed playlists with a generic list icon; now each row shows the
playlist's cover art (falling back to the icon when there's none), so you can
tell them apart at a glance when adding a song.

- web (modals.js): 34px cover thumbnail per row.
- android (PlaylistPickerSheet): 40dp AsyncImage cover, coverUrl passed from AppNavigation.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/ui/modals.js

@@ -87,7 +87,11 @@ export async function openPlModal(songs) {
     }
     S.cachedPlaylists.forEach(pl => {
       const row = document.createElement('div'); row.className = 'pl-row';
-      row.innerHTML = `<svg width="14" height="14" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><line x1="8" y1="6" x2="21" y2="6"/><line x1="8" y1="12" x2="21" y2="12"/><line x1="8" y1="18" x2="21" y2="18"/></svg>
+      const cv = pl.coverArt ? coverUrl(pl.coverArt, 96) : null;
+      const inner = cv
+        ? `<img src="${cv}" alt="" style="width:100%;height:100%;object-fit:cover" onerror="this.remove()">`
+        : '<svg width="14" height="14" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><line x1="8" y1="6" x2="21" y2="6"/><line x1="8" y1="12" x2="21" y2="12"/><line x1="8" y1="18" x2="21" y2="18"/></svg>';
+      row.innerHTML = `<span style="width:34px;height:34px;border-radius:6px;flex-shrink:0;background:var(--surface2);display:flex;align-items:center;justify-content:center;overflow:hidden;color:var(--text3)">${inner}</span>
         <span>${esc(pl.name)}</span><span style="margin-left:auto;font-size:11px;color:var(--text3)">${pl.songCount} Titel</span>`;
       row.onclick = () => addSongsToPlaylist(pl.id, pl.name);
       list.appendChild(row);