feat(poimen): consolidate into single multi-source ArgoCD app

- Merge poimen-workflows + poimen-memory + db + frontend into one app
- Delete duplicate apps: poimen-workflows, poimen-memory-app (kubectl done)
- Delete poimen-memory ArgoCD app file (replaced by multi-source source 2)
- Delete poimen-memory-database (replaced by source 3 → k8s/infra/poimen/)
- Move memory-db CNPG cluster to k8s/infra/poimen/ (isolated from other tenants)
- Remove memory-db from k8s/infra/databases/kustomization.yaml
- Add frontend manifests (Deployment, Service, Ingress) to k8s/apps/poimen/
- Add frontend NetworkPolicy: egress to api-gw (api:8080), memory (poimen:8080),
  Gotify (notifications:80), Authentik (iam:9000/9443), DNS (kube-system:53)
- Sync-wave -1 on CNPG cluster ensures DB ready before app pods (wave 0)
- Image updater: workflows + memory + frontend tracked in one annotation block
- poimen-toolkit stays separate (CRD management, independent rollback)

k8s/apps/poimen/frontend-ingress.yaml

@@ -0,0 +1,24 @@
+apiVersion: networking.k8s.io/v1
+kind: Ingress
+metadata:
+  name: poimen-frontend
+  namespace: poimen
+  annotations:
+    # Next.js SSE + LLM streaming responses need long timeouts + no buffering.
+    nginx.ingress.kubernetes.io/proxy-read-timeout: "3600"
+    nginx.ingress.kubernetes.io/proxy-send-timeout: "3600"
+    nginx.ingress.kubernetes.io/proxy-buffering: "off"
+    nginx.ingress.kubernetes.io/proxy-body-size: "10m"
+spec:
+  ingressClassName: nginx
+  rules:
+    - host: poimen.riotpiao.com
+      http:
+        paths:
+          - path: /
+            pathType: Prefix
+            backend:
+              service:
+                name: poimen-frontend
+                port:
+                  number: 3000