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/httpapi/handlers_registry.go

@@ -0,0 +1,59 @@
+package httpapi
+
+import (
+	"net/http"
+
+	"cloudipvalidator/internal/db"
+)
+
+// handleAdminRegistry lists every address ever submitted to the check
+// queue, each with a summary of its accumulated check history — the
+// durable record that survives an address being deleted from ip_queue and
+// later re-added. See migrations/0007_ip_registry.sql.
+func (s *Server) handleAdminRegistry(w http.ResponseWriter, r *http.Request) {
+	items, err := s.DB.ListRegistry(r.Context())
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, err.Error())
+		return
+	}
+	out := make([]registryDTO, len(items))
+	for i, it := range items {
+		out[i] = registrySummaryToDTO(it)
+	}
+	writeJSON(w, http.StatusOK, out)
+}
+
+// handleAdminRegistryHistory returns one address's registry record plus its
+// full retained check history (across every cycle still kept — see
+// db.PruneRegistryHistory / settings.history_retention_cycles), newest
+// cycle first.
+func (s *Server) handleAdminRegistryHistory(w http.ResponseWriter, r *http.Request) {
+	address := r.PathValue("ip")
+	summary, err := s.DB.GetRegistryByAddress(r.Context(), address)
+	if err != nil {
+		writeDBError(w, err)
+		return
+	}
+	checks, err := s.DB.ListChecksForRegistry(r.Context(), summary.ID, nil)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, err.Error())
+		return
+	}
+	writeJSON(w, http.StatusOK, struct {
+		Registry registryDTO `json:"registry"`
+		Checks   []db.Check  `json:"checks"`
+	}{registrySummaryToDTO(*summary), checks})
+}
+
+func registrySummaryToDTO(s db.RegistrySummary) registryDTO {
+	return registryDTO{
+		IPAddress:     s.IPAddress,
+		FirstSeenAt:   s.FirstSeenAt,
+		LastSeenAt:    s.LastSeenAt,
+		TotalCycles:   s.TotalCycles,
+		LastResult:    s.LastResult,
+		LastCheckedAt: s.LastCheckedAt,
+		InQueue:       s.InQueue,
+		CurrentState:  s.CurrentState,
+	}
+}