Add Gitea self-hosted git/CI/registry to replace GitHub

Deploy Gitea via Helm with dedicated CloudNativePG database,
in-cluster Actions runner (DinD), and built-in container registry.
ArgoCD repoURLs updated to use in-cluster Gitea SSH. Preview
ApplicationSet switched from GitHub PR generator to Gitea PR
generator. App images now pull from gitea.coreworlds.io registry.

Remaining setup after deploy: seal runner token, ArgoCD API token,
and registry pull secret once Gitea is running. Add ArgoCD deploy
key to Gitea repo settings.

infra/kubernetes/argocd/appsets/previews.yaml

@@ -8,9 +8,13 @@ spec:
   goTemplateOptions: ["missingkey=error"]
   generators:
     - pullRequest:
-        github:
-          owner: lazorgurl
+        gitea:
+          owner: julia
           repo: homelab
+          api: http://gitea-http.platform.svc:3000
+          tokenRef:
+            secretName: argocd-gitea-token
+            key: token
         requeueAfterSeconds: 60
   template:
     metadata:
@@ -18,7 +22,7 @@ spec:
     spec:
       project: default
       source:
-        repoURL: git@github.com:lazorgurl/homelab.git
+        repoURL: ssh://git@gitea-ssh.platform.svc:2222/julia/homelab.git
         targetRevision: "{{ .branch }}"
         path: apps/*/k8s/overlays/preview
         kustomize: