fix(pipeline): harden upstream resilience and production shutdown

DoH через DoWithRetry; CDN preview через UpstreamHTTPDo; частичный fail CDN (EVOBGP_CDN_PARTIAL_OK); безопасный доступ к Job.Meta; drain jobs при SIGTERM; ValidateProductionEnforce при EVOBGP_PRODUCTION=1.

Co-authored-by: Cursor <[email protected]>

internal/jobs/maintenance_worker.go

@@ -21,14 +21,13 @@ func (w *Worker) runMaintenancePolicy(j *Job) {
 		j.Fail("postgresql not configured")
 		return
 	}
-	policyID, _ := j.Meta["policy_id"].(string)
-	policyID = strings.TrimSpace(policyID)
+	policyID := strings.TrimSpace(j.metaString("policy_id"))
 	if policyID == "" {
 		j.Fail("missing policy_id in job meta")
 		return
 	}
-	dryRun, _ := j.Meta["dry_run"].(bool)
-	actor, _ := j.Meta["actor_prefix"].(string)
+	dryRun := j.metaBool("dry_run")
+	actor := j.metaString("actor_prefix")
 	ctx, cancel := j.workContext()
 	defer cancel()