Cut over ArgoCD to Gitea: update all repoURLs and PR generator

Switch app-of-apps, platform, apps, and previews ApplicationSets
to read from in-cluster Gitea (gitea-helm-ssh.platform.svc:2222).
Previews now use Gitea PR generator instead of GitHub.

infra/kubernetes/argocd/app-of-apps.yaml

@@ -8,7 +8,7 @@ metadata:
 spec:
   project: default
   source:
-    repoURL: git@github.com:lazorgurl/homelab.git
+    repoURL: ssh://git@gitea-helm-ssh.platform.svc:2222/lazorgurl/homelab.git
     targetRevision: main
     path: infra/kubernetes/argocd
   destination: