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/_ui/worker-status.tsx

@@ -0,0 +1,34 @@
+"use client";
+
+import { useEffect, useState } from "react";
+
+/** Live worker liveness in the masthead — polls /api/worker (heartbeat recency). */
+export function WorkerStatus() {
+  const [online, setOnline] = useState<boolean | null>(null);
+
+  useEffect(() => {
+    let alive = true;
+    async function check() {
+      try {
+        const d = await (await fetch("/api/worker")).json();
+        if (alive) setOnline(!!d.online);
+      } catch {
+        if (alive) setOnline(false);
+      }
+    }
+    check();
+    const id = setInterval(check, 10000);
+    return () => {
+      alive = false;
+      clearInterval(id);
+    };
+  }, []);
+
+  const label = online === null ? "…" : online ? "listening" : "offline";
+  return (
+    <div className={`worker-status${online === false ? " off" : ""}`}>
+      <span className="live-dot" />
+      Worker · {label}
+    </div>
+  );
+}