ui+server: P2-18d pending hosts dashboard panel + expiry sweeper

Dashboard handler loads ListPendingHosts(now); template renders a
warn-bordered panel above the host table with hostname, OS/arch,
fingerprint (selectable / copyable), source IP, age, expiry. Each
row carries an inline accept form (repo URL/user/password) plus a
Reject button. cmd/server adds a 60s ticker calling
DeleteExpiredPendingHosts so 1h-stale rows drop off.

cmd/server/main.go

@@ -156,6 +156,10 @@ func run() error {
 	// shouldn't, but the queue exists either way).
 	pendingDrainTick := time.NewTicker(30 * time.Second)
 	defer pendingDrainTick.Stop()
+	// Pending-hosts expiry sweeper: drops announce rows past their 1h
+	// ceiling so the dashboard panel doesn't accumulate stale entries.
+	pendingExpiryTick := time.NewTicker(60 * time.Second)
+	defer pendingExpiryTick.Stop()
 	mt := maintenance.New(st)
 	go func() {
 		for {
@@ -176,6 +180,10 @@ func run() error {
 				}
 			case <-pendingDrainTick.C:
 				srv.DrainAllDue(ctx)
+			case <-pendingExpiryTick.C:
+				if n, err := st.DeleteExpiredPendingHosts(ctx, time.Now().UTC()); err == nil && n > 0 {
+					slog.Info("expired pending hosts swept", "n", n)
+				}
 			case <-maintenanceTick.C:
 				decisions, err := mt.Decide(ctx, time.Now().UTC())
 				if err != nil {