feat: deploy to Frostmoln production

The AWS deploy-prod job has failed since CI left AWS (no k8s.unbound.se
context on the runners). Deploys now go to the Frostmoln production
cluster (namespace sites), the way Shiny deploys to Frostmoln staging.

Frostmoln enforces restricted Pod Security, so the served image is
nginx-unprivileged (uid 101, port 8080) with a matching securityContext.
The ALB ingress becomes a Traefik one with a Let's Encrypt certificate.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ma8eHhW59hLAJuLzBnLvUu

default.conf

@@ -1,5 +1,5 @@
 server {
-    listen       80;
+    listen       8080;
     server_name  localhost;
 
     access_log /dev/stdout combined;