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>

deploy/docker/control-api/control-api.docker.example.yaml

@@ -26,6 +26,7 @@ orchestrator:
   lease_ttl_seconds: 180
   heartbeat_timeout_seconds: 30
   fip_settle_seconds: 0
+  fip_scan_interval_seconds: 0
 
 aggregation:
   missing_counts_as_fail: true