feat: deploy n8n on the cluster

The runtime for the estate's autonomous agents. Postgres as a StatefulSet with
its own claim, n8n behind a cert-manager certificate and the nginx ingress, and
both secrets in Vault behind an AppRole scoped to n8n/* alone.

The certificate is issued into the cluster rather than copied into the repo, so
the private key never reaches git. The CA certificate is committed and mounted
as NODE_EXTRA_CA_CERTS, so a workflow can reach keycloak and the domain
gateways without anyone disabling verification to make it work.

One replica and strategy: Recreate, both deliberate — n8n needs Redis and queue
mode before a second scheduler is safe, and a ReadWriteOnce volume deadlocks a
rolling update.

N8N_ENCRYPTION_KEY is generated once and kept in Vault. Regenerating it does not
re-encrypt the stored credentials, it orphans them.

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

k8s/n8n/pvc.yaml

@@ -0,0 +1,13 @@
+# n8n keeps its own state here — including the SQLite of an unconfigured
+# install, which is not used since the database is Postgres, but also binary
+# data and anything a node writes. Small, and it must survive a restart.
+apiVersion: v1
+kind: PersistentVolumeClaim
+metadata:
+  name: n8n-data
+  namespace: n8n
+spec:
+  accessModes: ["ReadWriteOnce"]
+  resources:
+    requests:
+      storage: 2Gi