feat: add ArgoCD Application and k8s manifests for frontend

- application.yaml: ArgoCD Application resource (manual sync for now,
  same pattern as nextgen-be)
- manifests/: namespace, deployment, service, ingress

manifests/03-ingress.yaml

@@ -0,0 +1,24 @@
+apiVersion: networking.k8s.io/v1
+kind: Ingress
+metadata:
+  name: nextgen-fe
+  namespace: nextgen-fe
+  annotations:
+    kubernetes.io/ingress.class: "nginx"
+    # TLS terminates at the Hetzner Load Balancer, not here — this Ingress
+    # only ever sees plain HTTP. Without this, ingress-nginx may still try
+    # to force an HTTPS redirect and create a loop with the LB.
+    nginx.ingress.kubernetes.io/ssl-redirect: "false"
+spec:
+  ingressClassName: nginx
+  rules:
+    - host: rex24-nextgen.worker.helmholz.cloud
+      http:
+        paths:
+          - path: /
+            pathType: Prefix
+            backend:
+              service:
+                name: nextgen-fe
+                port:
+                  number: 80