Add k8s Gitea deployment (migration target for git.unkin.net) (#309)

Stand up the git.unkin.net forge on k8s to replace the Puppet VM. Deployed HA-shaped to match what the VM already runs (multi-replica on shared storage + external DB/cache), so this is genuine multi-replica HA rather than single-replica failover. Serves a temporary git2.k8s.syd1.au.unkin.net host; the git.unkin.net cutover is staged in docs/gitea-migration.md.

- add apps/base/gitea: namespace, CNPG gitea-postgres (2 instances, S3 backup bucket cnpg-gitea, nightly 04:00/30d), pgbouncer pooler, standalone Valkey (session/cache/queue, AOF), VaultAuth + VaultStaticSecrets, Gateway + HTTPRoute
- add apps/overlays/au-syd1/gitea: official Gitea chart 12.6.0 (app 1.26.2, rootless, 2 replicas) via helm-through-kustomize; RWX CephFS repo storage, external CNPG + Valkey, Actions disabled, container registry disabled (moved to artifactapi), Authentik OIDC with auto-register/account-linking; SSH via LoadBalancer VIP 198.18.200.10:2222
- register gitea in the platform ApplicationSet + AppProject
- add docs/gitea-migration.md staged cutover plan (VM Postgres->CNPG dump/restore, DNS in main.unkin.net zone, consumer checklist, rollback)

Depends on: terraform-authentik gitea OIDC app, and terraform-artifactapi ^gitea/ dockerhub allowlist (both separate PRs). One-time Vault seeds are listed in the migration doc.

Reviewed-on: #309
Co-authored-by: Ben Vincent <ben@unkin.net>
Co-committed-by: Ben Vincent <ben@unkin.net>

apps/base/bind-internal/authoritative/records.yaml

@@ -20,6 +20,32 @@ spec:
     # identity.unkin.net hostname there.
     - 198.18.200.4
 ---
+# PRODUCTION CUTOVER RECORD — intentionally commented out.
+# git.unkin.net currently resolves to the LIVE VM forge (HAProxy VRRP VIP
+# 198.18.19.17), which holds every repo the estate depends on. Uncommenting this
+# repoints the whole org's git.unkin.net at the new k8s Gitea gateway VIP, so it
+# is the FINAL step of the forge migration — gated on the data migration (gitea
+# dump/restore + SECRET_KEY copy) in argocd-apps docs/gitea-migration.md.
+# NOTE: the live git.unkin.net answer is served by the puppet DNS master today
+# (profiles::dns::master, records from PuppetDB); this k8s apex zone holds only
+# SOA+NS + a few DNSRecords so far. Confirm the k8s bind cluster is the live
+# authority for unkin.net (or update the puppet record instead) before relying
+# on this CR at cutover.
+# ---
+# apiVersion: bind.unkin.net/v1alpha1
+# kind: DNSRecord
+# metadata:
+#   name: git-dns-internal
+#   namespace: bind-internal
+# spec:
+#   zoneRef: unkin-net
+#   name: git
+#   type: A
+#   ttl: 600
+#   values:
+#     # traefik-internal gateway VIP; the gitea Gateway serves git.unkin.net there.
+#     - 198.18.200.4
+---
 apiVersion: bind.unkin.net/v1alpha1
 kind: DNSRecord
 metadata: