Add optional automatic check cycle (clear queue -> scan FIPs -> wait -> repeat)

An admin-controlled scenario that repeats what the operator does by hand:
clear the IP queue, scan and enqueue all free Floating IPs, wait until every
queued address reaches a terminal state (so results are in the Registry),
then wait a configurable interval and start over.

- control-api: new auto_cycle singleton table (migration 0008) holding
  enabled/interval/max-run settings and persisted phase state, so the cycle
  survives restarts; engine in orchestrator/autocycle.go driven from the
  existing loop tick with an injectable "now" for deterministic tests.
- Interval (default 1h, min 60s) and max wait (default unlimited, timeout
  outcome) are runtime settings, never hardcoded.
- The periodic fip_scan_interval_seconds scan is skipped while the cycle is
  enabled. An emptied queue mid-cycle counts as finished; stopping during
  the pause keeps the last cycle's outcome.
- API: GET/PUT /api/v1/admin/auto-cycle, POST .../start, POST .../stop.
- admin-dashboard: "Автоматический цикл" panel on /settings and an
  "Автоцикл активен" indicator on /overview.
- Tests for db, orchestrator, httpapi and dashboard; run-local-e2e.sh now
  exercises a full auto cycle; docs updated; bin/ rebuilt with refreshed
  SHA256SUMS.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

cmd/control-api/main.go

@@ -109,6 +109,7 @@ func runOrchestratorLoop(ctx context.Context, orch *orchestrator.Orchestrator, c
 			return
 		case <-ticker.C:
 			orch.Tick(ctx)
+			orch.AutoCycleStep(ctx)
 		case <-heartbeatTicker.C:
 			if err := orch.SweepStaleHeartbeats(ctx); err != nil {
 				log.Error("sweep stale heartbeats", "err", err)
@@ -117,6 +118,14 @@ func runOrchestratorLoop(ctx context.Context, orch *orchestrator.Orchestrator, c
 				log.Error("sweep stale site heartbeats", "err", err)
 			}
 		case <-scanTickerC:
+			// The auto-cycle owns the queue while enabled: a periodic scan
+			// would add addresses in the middle of a cycle.
+			ac, err := orch.GetAutoCycle(ctx)
+			if err != nil {
+				log.Error("read auto-cycle before periodic scan, scanning anyway", "err", err)
+			} else if ac.Enabled {
+				continue
+			}
 			if _, _, err := orch.ScanFloatingIPs(ctx); err != nil {
 				log.Error("scan floating ips", "err", err)
 			}