feat: deploy to Frostmoln production (#243)

Moves the production deploy from AWS to the Frostmoln production cluster (namespace `sites`).

- `deploy-prod` (AWS) has failed since CI left AWS: the runners have no `k8s.unbound.se` context, so the site on AWS still runs an older image. It's replaced by `deploy-prod-frostmoln`, the same pattern as Shiny's `deploy-frostmoln-staging`: `FROSTMOLN_PRODUCTION_DEPLOY_KEY` + `FROSTMOLN_PRODUCTION_CLUSTER_ID` (org), `BUILDTOOLS_FROSTMOLN_PRODUCTION` (org, target `prod-frostmoln`), `deploy prod-frostmoln -n sites`.
- Frostmoln enforces restricted Pod Security: the served image is `nginxinc/nginx-unprivileged` (uid 101, port 8080), with a matching securityContext; the Service is ClusterIP.
- `ingress-prod.yaml` (ALB) → `ingress-prod-frostmoln.yaml` (Traefik, Let's Encrypt).

Checked locally: the image serves `/health` and `/` (200) as uid 101 with all capabilities dropped.

**Merge after** infra's `feat/frostmoln-production-sites` is applied (namespace + org secret). The hostnames keep pointing at AWS until the Route 53 switch, a separate step; the certificate is issued after that.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

https://claude.ai/code/session_01Ma8eHhW59hLAJuLzBnLvUu
Reviewed-on: #243

k8s/deploy.yaml

@@ -22,6 +22,11 @@ spec:
       labels:
         app.kubernetes.io/name: unbound-site
     spec:
+      securityContext:
+        runAsNonRoot: true
+        runAsUser: 101
+        seccompProfile:
+          type: RuntimeDefault
       affinity:
         podAntiAffinity:
           preferredDuringSchedulingIgnoredDuringExecution:
@@ -39,14 +44,18 @@ spec:
         readinessProbe:
           httpGet:
             path: /health
-            port: 80
+            port: 8080
           initialDelaySeconds: 5
           periodSeconds: 5
           timeoutSeconds: 5
         imagePullPolicy: Always
         image: ${IMAGE}
         ports:
-        - containerPort: 80
+        - containerPort: 8080
+        securityContext:
+          allowPrivilegeEscalation: false
+          capabilities:
+            drop: ["ALL"]
         resources:
           requests:
             cpu: 5m
@@ -63,9 +72,8 @@ metadata:
   labels:
     app.kubernetes.io/name: unbound-site
 spec:
-  type: NodePort
   selector:
     app.kubernetes.io/name: unbound-site
   ports:
   - port: 80
-    targetPort: 80
+    targetPort: 8080