feat: deploy to Frostmoln production (#3100)

Part of the dancefinder.unbound.se cutover to Frostmoln Production (infra: unboundsoftware/infra#1896, already applied).

- Replaces the AWS `deploy-prod` job (failing since CI left AWS) with `deploy-prod-frostmoln` (`deploy prod-frostmoln -n dancefinder`), as schemas did.
- Restricted securityContext (runAsNonRoot, drop ALL, seccomp RuntimeDefault) and `imagePullSecrets: oci-registry` (Platform registry).
- Switches to `nginxinc/nginx-unprivileged` (same pin as schemas-app), listening on 8080 as uid 101; the Service keeps port 80. Traefik Ingress for `/`, PDB, HPA moved to `-prod-frostmoln`; ALB Ingress dropped; Service ClusterIP.

Merging deploys to Frostmoln only; DNS still points at AWS until the cutover.

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

https://claude.ai/code/session_01H6eVuR4Yt3m7TbDTDwyZJi
Reviewed-on: #3100

Dockerfile

@@ -12,7 +12,7 @@ COPY . /build
 RUN npm run postinstall && npm run generate && npm run lint
 #RUN yarn start:ci & yarn wait && yarn test:cypress
 
-FROM amd64/nginx:1.31.7@sha256:227f31dac037a2f1cdbd17ca9eec940a76c6c1b3187f5285eca2c3edb5d19c31
+FROM nginxinc/nginx-unprivileged:1.31.7@sha256:94193d5c4c5df716f412bb08eb97956d98fe6b59886f0bc57d6d3a3402a88a02
 MAINTAINER Joakim Olsson <joakim@unbound.se>
 
 COPY --from=builder /build/.output/public/ /usr/share/nginx/html/