Extend LE *.unkin.net wildcard to arrstack + authentik (reflect into gitea) (#418)

## Why

#417 stood up the central Let's Encrypt `*.unkin.net` wildcard (Certificate `wildcard-unkin-net` in `cert-manager`, secret `wildcard-unkin-net-tls`, emberstack-reflected). This wires the remaining single-label public hosts onto that publicly-trusted leaf instead of the internal Vault-PKI CA.

A `*.unkin.net` wildcard matches **single-label** subdomains only, so cluster hostnames under `*.k8s.syd1.au.unkin.net` are deliberately left on `vault-issuer`.

> Note: PR #417 already merged to `main`, so this is no longer stacked — it targets `main` directly.

## How

- **cert-manager**: reflect `wildcard-unkin-net-tls` into `arrstack`, `authentik`, `gitea` (appended to both reflector namespace lists → `cheeztv,arrstack,authentik,gitea`).
- **arrstack**: repoint the public `arrproxy` gateway listener (`arrstack.unkin.net`) `certificateRefs` → `wildcard-unkin-net-tls`; drop its `cert-manager.io/*` vault-issuer annotations.
- **authentik**: repoint the `identity.unkin.net` https listener → `wildcard-unkin-net-tls`. The `identity.k8s.syd1.au.unkin.net` listeners keep `authentik-tls` (vault-issuer), so the gateway `common-name` is retargeted to that cluster host. `authentik-ldap` gateway untouched.
- **gitea**: secret **reflected only**; `git.unkin.net` cutover deferred (no manifest change), same deferred pattern as fafflix.

## Validation

- `kustomize build` OK for cert-manager / arrstack / authentik / gitea overlays.
- `kubeconform` all valid (0 invalid, 0 errors) across the four overlays.
- Verified no `*.k8s.syd1.au.unkin.net` listener lost its vault-issuer wiring.

Reviewed-on: #418
Co-authored-by: unkin-agent <unkin-agent@unkin.net>
Co-committed-by: unkin-agent <unkin-agent@unkin.net>

apps/base/arrstack/arrproxy/gateway.yaml

@@ -1,9 +1,11 @@
 ---
 # External (DMZ) front for the arrstack, served on arrstack.unkin.net via the
-# external Traefik (LB VIP 198.18.199.0). cert-manager mints arrproxy-gateway-tls
-# (CN arrstack.unkin.net) off the internal Vault-PKI CA. The apex arrstack.unkin.net
-# A record lives in the bind-operator unkin.net zone (bind-internal/authoritative),
-# NOT external-dns, so no external-dns annotation here.
+# external Traefik (LB VIP 198.18.199.0). The apex arrstack.unkin.net A record
+# lives in the bind-operator unkin.net zone (bind-internal/authoritative), NOT
+# external-dns, so no external-dns annotation here. Public TLS is terminated with
+# the real Let's Encrypt *.unkin.net wildcard, centrally minted once in the
+# cert-manager namespace (Certificate wildcard-unkin-net) and reflected into this
+# namespace by the emberstack reflector as wildcard-unkin-net-tls, not Vault PKI.
 apiVersion: gateway.networking.k8s.io/v1
 kind: Gateway
 metadata:
@@ -11,9 +13,6 @@ metadata:
     traefik.io/instance: external
   annotations:
     argocd.argoproj.io/sync-wave: "2"
-    cert-manager.io/cluster-issuer: vault-issuer
-    cert-manager.io/common-name: arrstack.unkin.net
-    cert-manager.io/private-key-size: "4096"
   name: arrproxy
   namespace: arrstack
 spec:
@@ -38,4 +37,4 @@ spec:
         certificateRefs:
           - group: ""
             kind: Secret
-            name: arrproxy-gateway-tls
+            name: wildcard-unkin-net-tls