logging: deploy logviewer v0.1.0 behind oauth2-proxy (#404)

## Why

The logviewer UI gives browser access to the ClickHouse log store (`logreader` user). It must only be reachable by authorized users, so it sits behind an Authentik-gated oauth2-proxy front at https://logviewer.unkin.net, mirroring the arrstack front-door and mediamover/pdbmux gateway patterns.

## Changes

- Adds the logviewer Deployment (1 replica, `docker-internal/logviewer:v0.1.0`) reading ClickHouse at `clickhouse-logs` via the existing `clickhouse-logreader` Secret, `/healthz` probes, nonroot securityContext
- Adds an oauth2-proxy (quay.io/oauth2-proxy/oauth2-proxy:v7.15.3) front with issuer `https://identity.unkin.net/application/o/logviewer/`, `ak_groups` claim, allowed group `akP-logviewer-admin`, internal-CA trust via the combine-certs initContainer
- Syncs kv `kubernetes/namespace/logging/default/oauth-credentials` into the `logviewer-oauth-credentials` Secret via the existing `default` VaultAuth (kv path already seeded; no terraform-vault change needed)
- Adds ClusterIP Services for the app and the oauth2-proxy front door
- Adds internal Gateway + HTTPRoutes for `logviewer.unkin.net` (vault-issuer cert, external-dns -> 198.18.200.4, http->https redirect)
- Registers `logviewer/` in the logging base kustomization

## Dependency

Login requires the Authentik `logviewer` provider/application from terraform-authentik PR #21. This PR is safe to merge first: the VSO secret sync and the deployment come up regardless; OIDC login only works once #21 is applied.

Validated with `kustomize build` (base + au-syd1 overlay) and kubeconform (49/49 valid).

Reviewed-on: #404
Co-authored-by: unkin-agent <unkin-agent@unkin.net>
Co-committed-by: unkin-agent <unkin-agent@unkin.net>

apps/base/logging/logviewer/httproute.yaml

@@ -0,0 +1,49 @@
+---
+apiVersion: gateway.networking.k8s.io/v1
+kind: HTTPRoute
+metadata:
+  name: logviewer-http-redirect
+  namespace: logging
+spec:
+  hostnames:
+    - logviewer.unkin.net
+  parentRefs:
+    - group: gateway.networking.k8s.io
+      kind: Gateway
+      name: logviewer
+      sectionName: http
+  rules:
+    - filters:
+        - type: RequestRedirect
+          requestRedirect:
+            scheme: https
+            statusCode: 301
+      matches:
+        - path:
+            type: PathPrefix
+            value: /
+---
+apiVersion: gateway.networking.k8s.io/v1
+kind: HTTPRoute
+metadata:
+  name: logviewer
+  namespace: logging
+spec:
+  hostnames:
+    - logviewer.unkin.net
+  parentRefs:
+    - group: gateway.networking.k8s.io
+      kind: Gateway
+      name: logviewer
+      sectionName: https
+  rules:
+    - backendRefs:
+        - group: ""
+          kind: Service
+          name: logviewer-oauth2
+          port: 80
+          weight: 1
+      matches:
+        - path:
+            type: PathPrefix
+            value: /