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.

apps/web/k8s/base/gitea-pull-secret-sealed.yaml

@@ -0,0 +1,22 @@
+# PLACEHOLDER: Re-seal with Gitea registry credentials
+# kubectl create secret docker-registry gitea-pull-secret \
+#   --namespace apps \
+#   --docker-server=gitea.coreworlds.io \
+#   --docker-username=julia \
+#   --docker-password=<token> \
+#   --dry-run=client -o yaml | kubeseal --format yaml \
+#     --controller-namespace kube-system --controller-name sealed-secrets-helm
+---
+apiVersion: bitnami.com/v1alpha1
+kind: SealedSecret
+metadata:
+  name: gitea-pull-secret
+  namespace: apps
+spec:
+  encryptedData:
+    .dockerconfigjson: PLACEHOLDER_SEAL_ME
+  template:
+    metadata:
+      name: gitea-pull-secret
+      namespace: apps
+    type: kubernetes.io/dockerconfigjson