GitLab cross-site replication Phase 1c (stage 2): live streaming replication

Adds externalClusters connectionParameters + replica.self/primary/source
to all four Cluster CRs (home pg-gitlab/pg-praefect, VPS
pg-gitlab/pg-praefect), turning last commit's recovery-only replicas
into real CNPG streaming replicas - exact pattern already proven for
pg-authentik. TLS certs copied cross-cluster manually (kubectl, not
git, same as every other cross-cluster secret in this plan).

Also adds pg-gitlab-app/pg-praefect-app password sync (PushSecret home
-> Vault -> ExternalSecret VPS, Merge policy) - CNPG-generated
passwords stay in sync via WAL replication but the K8s Secret OBJECTS
never resync on their own, same gap already closed for pg-authentik-app.

VPS's standalone clusters were already destroyed and recreated as
recovery-mode replicas in the prior commit (with the user's explicit
help running the classifier-blocked kubectl delete) - this commit turns
on the actual streaming replication on top of that.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/gitlab/manifests/cnpg-cluster.yaml

@@ -80,3 +80,58 @@ spec:
 
   monitoring:
     enablePodMonitor: true
+
+  # GitLab cross-site replication Phase 1c stage 2 (see
+  # /home/scooby/.claude/plans/jiggly-snacking-iverson.md) - streaming
+  # replication to/from the VPS's pg-gitlab cluster, alongside (not
+  # replacing) the barmanObjectStore backup above. Exact pattern proven
+  # for pg-authentik (infrastructure/authentik/manifests/cnpg-cluster.yaml).
+  #
+  # Auth: reuses CNPG's own generated streaming_replica client cert,
+  # copied here manually as pg-gitlab-vps-{ca,replication} (kubectl, not
+  # git). sslmode: verify-ca (not verify-full) - the VPS's server cert is
+  # issued for its in-cluster DNS names, not the NodePort IP dialed here.
+  #
+  # Reachable via 100.108.113.41 (VPS's Netbird IP) - home reaching OUT
+  # to the VPS already works via the netbird-egress DaemonSet's route, no
+  # UniFi port-forward needed for this direction (only the reverse,
+  # VPS->home, needed that - see ha-postgres-nodeport.yaml).
+  externalClusters:
+    - name: home
+      connectionParameters:
+        host: pg-gitlab-rw
+        port: "5432"
+        dbname: gitlabhq_production
+        user: streaming_replica
+        sslmode: verify-ca
+      sslCert:
+        name: pg-gitlab-replication
+        key: tls.crt
+      sslKey:
+        name: pg-gitlab-replication
+        key: tls.key
+      sslRootCert:
+        name: pg-gitlab-ca
+        key: ca.crt
+    - name: vps
+      connectionParameters:
+        host: 100.108.113.41
+        port: "32444"
+        dbname: gitlabhq_production
+        user: streaming_replica
+        sslmode: verify-ca
+      sslCert:
+        name: pg-gitlab-vps-replication
+        key: tls.crt
+      sslKey:
+        name: pg-gitlab-vps-replication
+        key: tls.key
+      sslRootCert:
+        name: pg-gitlab-vps-ca
+        key: ca.crt
+
+  # Distributed topology: both sides agree home is primary today.
+  replica:
+    self: home
+    primary: home
+    source: home  # required unconditionally by the admission webhook even though home isn't replicating from anyone (self == primary)