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/appsets/platform.yaml

@@ -8,7 +8,7 @@ spec:
   goTemplateOptions: ["missingkey=error"]
   generators:
     - git:
-        repoURL: git@github.com:lazorgurl/homelab.git
+        repoURL: ssh://git@gitea-helm-ssh.platform.svc:2222/lazorgurl/homelab.git
         revision: main
         directories:
           - path: infra/kubernetes/platform/*
@@ -18,7 +18,7 @@ spec:
     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: "{{ .path.path }}"
       destination: