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>

worker/lyra_worker/main.py

@@ -16,6 +16,7 @@ from lyra_worker.registry import (
 from lyra_worker.scan import scan_chunk
 
 IDLE_SLEEP = 2.0
+HEARTBEAT_SECONDS = 15.0  # how often to stamp worker.heartbeat (its updatedAt = liveness)
 MONITOR_TICK_SECONDS = 60.0
 DISCOVER_TICK_SECONDS = 300.0  # check the discovery interval every 5 min (interval itself is hours)
 DEST_ROOT = "/music"  # must match run_pipeline's default library root
@@ -147,6 +148,7 @@ def run_forever() -> None:
     print("worker: waiting for jobs", flush=True)
     last_tick = 0.0
     last_discover_tick = 0.0
+    last_heartbeat = 0.0
     try:
         while True:
             # A transient DB connection loss (e.g. AdminShutdown when Postgres restarts) raises
@@ -157,6 +159,9 @@ def run_forever() -> None:
                 config = get_config(conn)
                 mcfg = MonitorConfig.from_config(config)
                 now = time.monotonic()
+                if now - last_heartbeat >= HEARTBEAT_SECONDS:
+                    _set_config(conn, "worker.heartbeat", "1")  # value irrelevant; updatedAt is the signal
+                    last_heartbeat = now
                 if mcfg.enabled and now - last_tick >= MONITOR_TICK_SECONDS:
                     try:
                         sweep(conn, browser, mcfg)