refactor: bootstrap/infra/ci separation (#27)

- Create bootstrap/ dir: cert-manager, traefik-routes, argo-rollouts,
  kargo, kargo-*-pipeline (not managed by Kargo promotion)
- infra/ now only: gitea, gitea-custom (promoted by Kargo)
- ci/ unchanged: gitea-runner (promoted by Kargo)
- Split kargo/credentials/ into dev/ and prod/ with separate ksops generators
- Remove kargo-credentials from AppSet (managed by Pulumi Go code)
- Update infra Warehouse: only gitea (was also argo-rollouts, cert-manager)
- Update infra Stage dev: only yaml-update for gitea version
- Fix test-env warehouse: valid subscription instead of empty array
- Update step numbers: bootstrap 1-5, infra 1-2

bootstrap/traefik-routes/manifests/namespaces.yaml

@@ -0,0 +1,14 @@
+# Ensure namespaces exist for cross-namespace middleware references
+apiVersion: v1
+kind: Namespace
+metadata:
+  name: gitea
+  labels:
+    name: gitea
+---
+apiVersion: v1
+kind: Namespace
+metadata:
+  name: kargo
+  labels:
+    name: kargo