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>

internal/dashboard/dto.go

@@ -41,6 +41,8 @@ type ipQueueItem struct {
 
 type check struct {
 	ID            int64
+	RegistryID    int64
+	CycleID       int
 	IPID          int64
 	IPAddress     string
 	AttemptNumber int
@@ -96,6 +98,33 @@ type clearQueueResponse struct {
 	Deleted []string `json:"deleted"`
 }
 
+type scanIPsResponse struct {
+	ScannedFree       int      `json:"scanned_free"`
+	Added             []string `json:"added"`
+	Requeued          []string `json:"requeued"`
+	Reordered         []string `json:"reordered"`
+	SkippedInProgress []string `json:"skipped_in_progress"`
+}
+
+// registryItem is one row of the durable per-address registry — see
+// httpapi's registryDTO. Survives an address being deleted from the check
+// queue and later re-added, unlike ipQueueItem above.
+type registryItem struct {
+	IPAddress     string     `json:"ip_address"`
+	FirstSeenAt   time.Time  `json:"first_seen_at"`
+	LastSeenAt    time.Time  `json:"last_seen_at"`
+	TotalCycles   int        `json:"total_cycles"`
+	LastResult    string     `json:"last_result"`
+	LastCheckedAt *time.Time `json:"last_checked_at"`
+	InQueue       bool       `json:"in_queue"`
+	CurrentState  string     `json:"current_state"`
+}
+
+type registryHistoryResponse struct {
+	Registry registryItem `json:"registry"`
+	Checks   []check      `json:"checks"`
+}
+
 type validatorDTO struct {
 	ValidatorID     string     `json:"validator_id"`
 	Hostname        string     `json:"hostname"`
@@ -128,7 +157,8 @@ type errorResponse struct {
 }
 
 type orchestratorSettingsDTO struct {
-	FIPSettleSeconds int `json:"fip_settle_seconds"`
+	FIPSettleSeconds       int `json:"fip_settle_seconds"`
+	HistoryRetentionCycles int `json:"history_retention_cycles"`
 }
 
 type inboundChecksDTO struct {