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: https://gitea.unbound.se/dancefinder/dancefinder-app/pulls/3100

k8s/ingress-prod.yaml

@@ -1,29 +0,0 @@
-apiVersion: networking.k8s.io/v1
-kind: Ingress
-metadata:
-  name: dancefinder-app-ingress
-  annotations:
-    alb.ingress.kubernetes.io/group.name: "default"
-    alb.ingress.kubernetes.io/group.order: "101"
-    alb.ingress.kubernetes.io/scheme: internet-facing
-    alb.ingress.kubernetes.io/target-type: instance
-    alb.ingress.kubernetes.io/listen-ports: '[{"HTTP": 80},{"HTTPS": 443}]'
-    alb.ingress.kubernetes.io/ssl-redirect: "443"
-    alb.ingress.kubernetes.io/healthcheck-path: "/health"
-    alb.ingress.kubernetes.io/healthcheck-interval-seconds: "30"
-    alb.ingress.kubernetes.io/healthcheck-timeout-seconds: "5"
-    alb.ingress.kubernetes.io/healthy-threshold-count: "2"
-    alb.ingress.kubernetes.io/unhealthy-threshold-count: "2"
-spec:
-  ingressClassName: "alb"
-  rules:
-    - host: "dancefinder.unbound.se"
-      http:
-        paths:
-          - path: /*
-            pathType: ImplementationSpecific
-            backend:
-              service:
-                name: dancefinder-app
-                port:
-                  number: 80