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/api/requests/route.ts

@@ -35,10 +35,11 @@ export async function POST(request: Request) {
 }
 
 export async function GET() {
-  const requests = await prisma.request.findMany({
-    orderBy: { createdAt: "desc" },
-    include: { job: true },
-  });
+  const [requests, releases] = await Promise.all([
+    prisma.request.findMany({ orderBy: { createdAt: "desc" }, include: { job: true } }),
+    prisma.monitoredRelease.findMany({ select: { artistName: true, album: true, rgMbid: true } }),
+  ]);
+  const rgByKey = new Map(releases.map((mr) => [`${mr.artistName} ${mr.album}`, mr.rgMbid]));
 
   return Response.json({
     requests: requests.map((r) => ({
@@ -47,6 +48,7 @@ export async function GET() {
       album: r.album,
       status: r.status,
       createdAt: r.createdAt,
+      rgMbid: rgByKey.get(`${r.artist} ${r.album}`) ?? null,
       job: r.job ? { state: r.job.state, currentStage: r.job.currentStage } : null,
     })),
   });