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/base/deployment.yaml

@@ -0,0 +1,91 @@
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: vncmail-plus
+  labels:
+    app: vncmail-plus
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      app: vncmail-plus
+  # RWO volumes can only mount to one pod — Recreate avoids a stuck rollout.
+  strategy:
+    type: Recreate
+  template:
+    metadata:
+      labels:
+        app: vncmail-plus
+    spec:
+      # The image runs as uid/gid 1001 (nextjs:nodejs) and the Dockerfile
+      # chowns /app/data to 1001. fsGroup makes the mounted PVCs writable by it.
+      securityContext:
+        fsGroup: 1001
+        runAsUser: 1001
+        runAsGroup: 1001
+      # ghcr package is private by default — see deploy/k8s/README.md to create
+      # this pull secret. Delete this block if you make the package public.
+      # NOTE: once CI moves to pushing registry.gitlab.vnc.biz images (the
+      # dev-auto-deploy phase of the GitLab pipeline), this needs to become a
+      # docker-registry secret for that registry instead — comments only,
+      # deliberately not renamed here, so this file stays a no-op today.
+      imagePullSecrets:
+        - name: ghcr-pull
+      containers:
+        - name: vncmail-plus
+          # Default/legacy value — CI overrides the image per-deploy via
+          # `kustomize edit set image`, so what's committed here never goes
+          # stale. For a one-off manual apply, pin a digest instead of :latest.
+          image: ghcr.io/brvncde-dotcom/vncmail-plus-dev:latest
+          imagePullPolicy: Always
+          ports:
+            - containerPort: 3000
+          envFrom:
+            - secretRef:
+                name: vncmail-env
+          env:
+            - name: HOSTNAME
+              value: "0.0.0.0"
+            - name: PORT
+              value: "3000"
+          readinessProbe:
+            httpGet:
+              path: /api/health
+              port: 3000
+            initialDelaySeconds: 10
+            periodSeconds: 10
+          livenessProbe:
+            httpGet:
+              path: /api/health
+              port: 3000
+            initialDelaySeconds: 25
+            periodSeconds: 30
+          resources:
+            requests:
+              cpu: 100m
+              memory: 256Mi
+            limits:
+              cpu: "1"
+              memory: 1Gi
+          volumeMounts:
+            - name: settings
+              mountPath: /app/data/settings
+            - name: admin
+              mountPath: /app/data/admin
+            - name: admin-state
+              mountPath: /app/data/admin-state
+            - name: telemetry
+              mountPath: /app/data/telemetry
+      volumes:
+        - name: settings
+          persistentVolumeClaim:
+            claimName: vncmail-settings
+        - name: admin
+          persistentVolumeClaim:
+            claimName: vncmail-admin
+        - name: admin-state
+          persistentVolumeClaim:
+            claimName: vncmail-admin-state
+        - name: telemetry
+          persistentVolumeClaim:
+            claimName: vncmail-telemetry