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>

dev/gitrepository.yaml

@@ -0,0 +1,14 @@
+# HTTPS with no credentials: the repo is anonymously readable over HTTPS on
+# gitea, so a deploy key would guard nothing while adding a Vault entry and a
+# gitea key to create by hand before anything deploys. TLS still gives integrity
+# and authenticity of the source.
+apiVersion: source.toolkit.fluxcd.io/v1
+kind: GitRepository
+metadata:
+  name: infra-n8n
+  namespace: n8n
+spec:
+  interval: 5m
+  url: https://gitea.sttlab.eu/stt/infra-n8n.git
+  ref:
+    branch: main