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/platform/traefik/kustomization.yaml

@@ -8,5 +8,6 @@ resources:
   - ingressroute-grafana.yaml
   - ingressroute-longhorn.yaml
   - ingressroute-harness.yaml
+  - ingressroute-gitea.yaml
   - certificate-internal.yaml
   - servicemonitor.yaml