feat(tls): migrate public ingress TLS from Traefik ACME to cert-manager

All prod IngressRoutes switch tls.certResolver to tls.secretName
backed by per-router Certificates (HTTP-01, letsencrypt-prod).
adguard-prod reuses the shared adguard-certs secret (also feeds
DoT :853); sync CronJob removed as redundant.

Traefik certificatesResolvers removed: its internal
acme-http@internal router hijacks HTTP-01 for every host while
enabled, blocking external solvers. Dormant files (kener,
downtify) converted for consistency but not applied; n8n
untouched per live-only rule.

nextcloud/k8s/routing/certificates.yaml

@@ -0,0 +1,12 @@
+apiVersion: cert-manager.io/v1
+kind: Certificate
+metadata:
+  name: nextcloud-prod-tls
+  namespace: nextcloud
+spec:
+  secretName: nextcloud-prod-tls
+  dnsNames:
+    - nextcloud.forust.xyz
+  issuerRef:
+    name: letsencrypt-prod
+    kind: ClusterIssuer