feat: real worker status, covers on Recently Pressed, library counter

- Worker stamps a throttled worker.heartbeat; GET /api/worker reports online
  from its updatedAt recency (DB-time); masthead shows a live listening/offline
  dot instead of a static decoration.
- /api/requests enriched with rgMbid; Recently Pressed shows cover thumbs.
- Library album count moved from the filter row into a section header.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web/src/app/design.css

@@ -342,3 +342,11 @@ nav.contents .sep { flex: 1; }
 }
 @keyframes toast-in { from { opacity: 0; transform: translateY(10px); } to { opacity: 1; transform: none; } }
 @media (prefers-reduced-motion: reduce) { .toast { animation: none; } }
+
+/* ── Worker status (live) ─────────────────────────────── */
+.worker-status.off { color: var(--graphite); }
+.worker-status.off .live-dot { background: var(--graphite); animation: none; }
+
+/* ── Recently-pressed thumbnail ───────────────────────── */
+.pressed li { align-items: center; }
+.pressed-thumb { width: 30px; height: 30px; flex-shrink: 0; }