feat(deploy): k8s manifests for microk8s (vncmail.sandbox.vnc.de)

Bulwark is stateful (local /app/data) — Vercel serverless (read-only fs)
crashes it. Deploy as a container with 4 persistent volumes on microk8s,
alongside bulwark.sandbox.vnc.de. Adds deploy/k8s/ (namespace, pvc, deployment,
service, ingress, secret template, runbook) + rewrites setup doc off Vercel.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

deploy/k8s/namespace.yaml

@@ -0,0 +1,6 @@
+apiVersion: v1
+kind: Namespace
+metadata:
+  name: vncmail
+  labels:
+    app.kubernetes.io/part-of: vnclagoon-suite