Add Floating IP scanning and a durable address registry with configurable history depth

Adds POST /api/v1/admin/ips/scan (plus an optional periodic ticker) to
discover free Floating IPs in the OpenStack project and feed them straight
into the check queue. More importantly, decouples check/event history from
ip_queue's lifecycle: a new ip_registry table (migration 0007) gives every
address ever submitted a durable identity, so deleting it from the queue no
longer destroys its history — it's still reachable via the new
GET /api/v1/admin/registry[/{ip}] endpoints and the dashboard's /registry
pages, with retention depth configurable in check cycles per address
(history_retention_cycles, 0 = unlimited).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

cmd/control-api/main.go

@@ -92,6 +92,17 @@ func runOrchestratorLoop(ctx context.Context, orch *orchestrator.Orchestrator, c
 	heartbeatTicker := time.NewTicker(interval * 2)
 	defer heartbeatTicker.Stop()
 
+	// Periodic floating-IP scanning is optional: a zero interval leaves
+	// scanTickerC nil, and a select on a nil channel simply never fires, so
+	// the loop falls back to manual-only scanning (POST
+	// /api/v1/admin/ips/scan) without a special-cased branch below.
+	var scanTickerC <-chan time.Time
+	if cfg.Orchestrator.FIPScanIntervalSeconds > 0 {
+		scanTicker := time.NewTicker(time.Duration(cfg.Orchestrator.FIPScanIntervalSeconds) * time.Second)
+		defer scanTicker.Stop()
+		scanTickerC = scanTicker.C
+	}
+
 	for {
 		select {
 		case <-ctx.Done():
@@ -105,6 +116,10 @@ func runOrchestratorLoop(ctx context.Context, orch *orchestrator.Orchestrator, c
 			if err := orch.SweepStaleSiteHeartbeats(ctx); err != nil {
 				log.Error("sweep stale site heartbeats", "err", err)
 			}
+		case <-scanTickerC:
+			if _, _, err := orch.ScanFloatingIPs(ctx); err != nil {
+				log.Error("scan floating ips", "err", err)
+			}
 		}
 	}
 }