feat(ci): GitLab CI/CD dev→prod pipeline, kustomize base+overlays

Multiple developers now work on this repo, and the only working deploy
trigger required pushing to GitHub - which contradicts the standing
GitLab-canonical policy for this repo - while every actual deploy was a
manual kubectl run against one environment (no prod exists at all).

Restructures deploy/k8s/ into base/ + overlays/{dev,prod}: overlays/dev
is a verified byte-for-byte no-op for the live sandbox (kubectl kustomize
diff against the old flat layout is empty), overlays/prod is scaffolded
but inert (placeholder hostname + JMAP_SERVER_URL, since neither a prod
hostname decision nor a prod Stalwart exist yet). deploy/k8s/ca/ (the
EJBCA internal CA) is untouched and never referenced by either overlay.

Adds .gitlab-ci.yml: verify (MR gate, no push/deploy) -> build+deploy-dev
(automatic on push to dev, one image name/tag-only environments, fixing
the old -dev/-beta naming split) -> promote (manual, protected
`production` environment, retags the exact dev digest via
`docker buildx imagetools create` - never rebuilds - and is left as a
documented TODO for the actual `kubectl apply` until prod is real).

Updates VNCMAIL-SETUP.md and deploy/k8s/README.md to describe the new
flow and correct the aspirational promotion description that assumed a
"production image" CI never actually built.

Also fixes a pre-existing lint error (no-control-regex false positive on
an intentional DN-sanitizing character class in lib/smime-ca/ejbca.ts)
that was blocking this commit's pre-commit hook - unrelated to this
change otherwise, confirmed already present on dev before this branch.

Runner/RBAC/registry setup is an infra prerequisite this commit cannot
provide - documented in the pipeline plan, not part of this diff.

deploy/k8s/overlays/prod/kustomization.yaml

@@ -0,0 +1,21 @@
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+namespace: vncmail-prod
+resources:
+  - ../../base
+  - namespace.yaml
+  # - secret.yaml   # create from secret.example.yaml; not committed
+
+patches:
+  - path: patch-ingress.yaml
+  - path: patch-deployment.yaml
+
+# NOT MEANT TO BE APPLIED AS COMMITTED. Scaffolding only (see the pipeline
+# plan's Phase C/D) — the tag below is an obviously-invalid placeholder;
+# the real promote job (.gitlab-ci.yml) resolves and pins an actual digest at
+# deploy time via `kubectl set image`, it never trusts whatever is checked
+# in here.
+images:
+  - name: ghcr.io/brvncde-dotcom/vncmail-plus-dev
+    newName: registry.gitlab.vnc.biz/gitlab-instance-b9b5cf2f/vncmail-plus
+    newTag: not-yet-promoted

deploy/k8s/overlays/prod/namespace.yaml

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

deploy/k8s/overlays/prod/patch-deployment.yaml

@@ -0,0 +1,9 @@
+# Basic HA. Still `strategy: Recreate` (inherited from base) since the PVCs
+# are RWO — 2 replicas doesn't buy zero-downtime rollouts by itself, only
+# tolerance for a node loss between deploys. Revisit if that's not enough.
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: vncmail-plus
+spec:
+  replicas: 2

deploy/k8s/overlays/prod/patch-ingress.yaml

@@ -0,0 +1,25 @@
+# PLACEHOLDER — the real production hostname has not been decided yet (see
+# VNCMAIL-SETUP.md / the pipeline plan). vncmail.CHANGEME.invalid is
+# deliberately unresolvable: applying this overlay as committed will not
+# issue a cert or route traffic anywhere. Replace both occurrences below,
+# and the matching TLS secretName, before Phase D (first real prod deploy).
+apiVersion: networking.k8s.io/v1
+kind: Ingress
+metadata:
+  name: vncmail-plus
+spec:
+  tls:
+    - hosts:
+        - vncmail.CHANGEME.invalid
+      secretName: vncmail-plus-prod-tls
+  rules:
+    - host: vncmail.CHANGEME.invalid
+      http:
+        paths:
+          - path: /
+            pathType: Prefix
+            backend:
+              service:
+                name: vncmail-plus
+                port:
+                  number: 80

deploy/k8s/overlays/prod/secret.example.yaml

@@ -0,0 +1,28 @@
+# Copy to secret.yaml, fill in real values, and apply. DO NOT commit secret.yaml
+# (it is gitignored). Generate SESSION_SECRET with:  openssl rand -base64 32
+#
+# JMAP_SERVER_URL is a PLACEHOLDER — there is no production Stalwart instance
+# yet. This overlay cannot go live (Phase D) until one exists and this value
+# points at it for real.
+apiVersion: v1
+kind: Secret
+metadata:
+  name: vncmail-env
+  namespace: vncmail-prod
+type: Opaque
+stringData:
+  # Core — connect to Stalwart over JMAP
+  JMAP_SERVER_URL: "https://REPLACE-ME-prod-stalwart-not-yet-deployed.invalid"
+  SESSION_SECRET: "REPLACE_ME__openssl_rand_base64_32"
+  # Branding (theme defaults to VNClagoon in code; these set name + logo)
+  APP_NAME: "VNCmail+"
+  APP_SHORT_NAME: "VNCmail+"
+  LOGIN_COMPANY_NAME: "VNClagoon"
+  LOGIN_LOGO_DARK_URL: "/branding/vncmail-wordmark-on-dark.svg"
+  LOGIN_LOGO_LIGHT_URL: "/branding/vncmail-wordmark-on-light.svg"
+  APP_LOGO_DARK_URL: "/branding/vncmail-wordmark-on-dark.svg"
+  APP_LOGO_LIGHT_URL: "/branding/vncmail-wordmark-on-light.svg"
+  LOGIN_LOGO_MAX_HEIGHT: "52"
+  # Housekeeping
+  BULWARK_UPDATE_CHECK: "off"
+  # Data dirs default to /app/data/* (mounted to the PVCs) — no need to set them.