Add identity.unkin.net internal DNS record (#256)

## Why

`identity.unkin.net` is configured as the Authentik OIDC issuer but has **no DNS record anywhere**, so in-cluster OIDC discovery fails (e.g. `argocd-server` → `lookup identity.unkin.net ... no such host`). Add an authoritative A record served by the internal bind system (bind-operator) so it resolves.

## Change

- New `DNSRecord/identity-dns-internal` → `198.18.200.4` (the traefik-internal gateway VIP, where the Authentik Gateway serves the `identity.unkin.net` hostname), in the `unkin-net` zone.
- Lives in the **`bind-internal` namespace** alongside the `BindZone`: the operator resolves `zoneRef`/`clusterRef`/`updateKeyRef` within the record's own namespace, so it can't live in the app (authentik) namespace.
- Wired into `apps/base/bind-internal/authoritative/kustomization.yaml`.
- `identity-dns-internal` name distinguishes this from the external DNS that Authentik will manage its own records from later.

## Validation

`kustomize build apps/base/bind-internal` + kubeconform (validates against the `dnsrecord_v1alpha1` schema): 57 valid, 0 invalid. pre-commit clean.

Reviewed-on: #256
Co-authored-by: Ben Vincent <ben@unkin.net>
Co-committed-by: Ben Vincent <ben@unkin.net>

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

@@ -6,4 +6,5 @@ resources:
   - cluster.yaml
   - tsigkey.yaml
   - zones.yaml
+  - records.yaml
   - acls.yaml

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

@@ -0,0 +1,21 @@
+# Individually-managed authoritative records for the unkin.net zone.
+# DNSRecords must live in the same namespace as their BindZone (the operator
+# resolves zoneRef/clusterRef/updateKeyRef within the record's namespace), so
+# these sit alongside the zone in bind-internal, not in the app namespace.
+---
+apiVersion: bind.unkin.net/v1alpha1
+kind: DNSRecord
+metadata:
+  # "internal" in the name distinguishes this from the external DNS that
+  # Authentik will manage its own records from later.
+  name: identity-dns-internal
+  namespace: bind-internal
+spec:
+  zoneRef: unkin-net
+  name: identity
+  type: A
+  ttl: 600
+  values:
+    # traefik-internal gateway VIP; the authentik Gateway serves the
+    # identity.unkin.net hostname there.
+    - 198.18.200.4