argocd: add Image Updater for auto-deploy on image push

- Install argocd-image-updater via Helm (wave 1)
- Configure Forgejo registry (anonymous pulls)
- Annotate apps for auto-update: api-gw, portfolio, management-service, queue-crd
- Uses newest-build strategy for commit SHA tags

k8s/argocd/apps/55-api-gateway.yaml

@@ -36,6 +36,10 @@ metadata:
     app.kubernetes.io/component: gateway
   annotations:
     argocd.argoproj.io/sync-wave: "7"
+    # ArgoCD Image Updater - auto-update on new image push
+    argocd-image-updater.argoproj.io/image-list: gw=forgejo.riotpiao.com/rock/api-gateway
+    argocd-image-updater.argoproj.io/gw.update-strategy: newest-build
+    argocd-image-updater.argoproj.io/write-back-method: argocd
 spec:
   project: homelab
   revisionHistoryLimit: 3