feat: add Clear Cache & Rebuild button for playlists in Admin UI

- New endpoint: POST /api/admin/playlists/{name}/clear-cache
- Clears Redis cache keys (items, matched tracks, missing tracks)
- Deletes file caches
- Triggers automatic rebuild with latest code (includes Spotify IDs)
- Added prominent button in Admin UI playlist table
- Shows confirmation dialog with details of what will be cleared

allstarr/wwwroot/index.html

@@ -1331,6 +1331,7 @@
                             </td>
                             <td class="cache-age">${p.cacheAge || '-'}</td>
                             <td>
+                                <button onclick="clearPlaylistCache('${escapeJs(p.name)}')">Clear Cache & Rebuild</button>
                                 <button onclick="matchPlaylistTracks('${escapeJs(p.name)}')">Match Tracks</button>
                                 <button onclick="prefetchLyrics('${escapeJs(p.name)}')">Prefetch Lyrics</button>
                                 <button onclick="viewTracks('${escapeJs(p.name)}')">View</button>
@@ -1672,6 +1673,26 @@
             }
         }
         
+        async function clearPlaylistCache(name) {
+            if (!confirm(`Clear cache and rebuild for "${name}"?\n\nThis will:\n• Clear Redis cache\n• Delete file caches\n• Rebuild with latest Spotify IDs\n\nThis may take a minute.`)) return;
+            
+            try {
+                showToast(`Clearing cache for ${name}...`, 'info');
+                const res = await fetch(`/api/admin/playlists/${encodeURIComponent(name)}/clear-cache`, { method: 'POST' });
+                const data = await res.json();
+                
+                if (res.ok) {
+                    showToast(`✓ ${data.message} (Cleared ${data.clearedKeys} cache keys, ${data.clearedFiles} files)`, 'success', 5000);
+                    // Refresh the playlists table after a delay to show updated counts
+                    setTimeout(fetchPlaylists, 3000);
+                } else {
+                    showToast(data.error || 'Failed to clear cache', 'error');
+                }
+            } catch (error) {
+                showToast('Failed to clear cache', 'error');
+            }
+        }
+        
         async function matchPlaylistTracks(name) {
             try {
                 showToast(`Matching tracks for ${name}...`, 'success');