k8s-gateway: swap helm repo to maintained fork

ori-edge/k8s_gateway is deprecated (last release Nov 2023, README
redirects to k8s-gateway/k8s_gateway). Chart name, fullnameOverride,
and service.clusterIP still supported, so this is a rolling upgrade.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

kubernetes/infrastructure/k8s-gateway/helmrelease.yaml

@@ -5,7 +5,7 @@ metadata:
   namespace: kube-system
 spec:
   interval: 24h
-  url: https://ori-edge.github.io/k8s_gateway/
+  url: https://k8s-gateway.github.io/k8s_gateway/
 ---
 # In-cluster authoritative resolver for renner.uno.
 #