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/oauth2-proxy-deployment.yaml

@@ -0,0 +1,132 @@
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: logviewer-oauth2
+  namespace: logging
+  annotations:
+    configmap.reloader.stakater.com/auto: "true"
+    secret.reloader.stakater.com/reload: "logviewer-oauth-credentials,vault-ca-cert"
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      app: logviewer-oauth2
+  strategy:
+    rollingUpdate:
+      maxUnavailable: 1
+    type: RollingUpdate
+  template:
+    metadata:
+      labels:
+        app: logviewer-oauth2
+    spec:
+      serviceAccountName: default
+      automountServiceAccountToken: false
+      securityContext:
+        runAsNonRoot: true
+        runAsUser: 65532
+        runAsGroup: 65532
+        fsGroup: 65532
+        seccompProfile:
+          type: RuntimeDefault
+      initContainers:
+        # identity.unkin.net serves a Vault-PKI cert; combine the system roots
+        # with the internal CA so oauth2-proxy's OIDC HTTP client trusts it.
+        - name: combine-certs
+          image: artifactapi.k8s.syd1.au.unkin.net/dockerhub/library/alpine:3
+          imagePullPolicy: IfNotPresent
+          command:
+            - sh
+            - -c
+            - cat /etc/ssl/certs/ca-certificates.crt /custom-ca/ca.crt > /combined-certs/ca-certificates.crt
+          volumeMounts:
+            - name: vault-ca-cert
+              mountPath: /custom-ca
+              readOnly: true
+            - name: combined-certs
+              mountPath: /combined-certs
+          securityContext:
+            allowPrivilegeEscalation: false
+            readOnlyRootFilesystem: true
+            capabilities:
+              drop:
+                - ALL
+          resources:
+            requests:
+              cpu: 50m
+              memory: 32Mi
+            limits:
+              cpu: 200m
+              memory: 64Mi
+      containers:
+        - name: oauth2-proxy
+          image: quay.io/oauth2-proxy/oauth2-proxy:v7.15.3
+          imagePullPolicy: IfNotPresent
+          ports:
+            - containerPort: 4180
+              name: http
+              protocol: TCP
+          envFrom:
+            - configMapRef:
+                name: logviewer-oauth2-env
+                optional: false
+          env:
+            - name: OAUTH2_PROXY_CLIENT_ID
+              valueFrom:
+                secretKeyRef:
+                  name: logviewer-oauth-credentials
+                  key: client_id
+            - name: OAUTH2_PROXY_CLIENT_SECRET
+              valueFrom:
+                secretKeyRef:
+                  name: logviewer-oauth-credentials
+                  key: client_secret
+            - name: OAUTH2_PROXY_COOKIE_SECRET
+              valueFrom:
+                secretKeyRef:
+                  name: logviewer-oauth-credentials
+                  key: cookie_secret
+          volumeMounts:
+            - name: combined-certs
+              mountPath: /etc/ssl/combined
+              readOnly: true
+          livenessProbe:
+            httpGet:
+              path: /ping
+              port: http
+            initialDelaySeconds: 10
+            periodSeconds: 30
+            timeoutSeconds: 5
+            failureThreshold: 3
+          readinessProbe:
+            httpGet:
+              path: /ready
+              port: http
+            initialDelaySeconds: 5
+            periodSeconds: 10
+            timeoutSeconds: 5
+            failureThreshold: 3
+          securityContext:
+            allowPrivilegeEscalation: false
+            readOnlyRootFilesystem: true
+            capabilities:
+              drop:
+                - ALL
+          resources:
+            requests:
+              cpu: 50m
+              memory: 64Mi
+            limits:
+              cpu: 500m
+              memory: 256Mi
+      volumes:
+        - name: vault-ca-cert
+          secret:
+            secretName: vault-ca-cert
+            items:
+              - key: ca.crt
+                path: ca.crt
+        - name: combined-certs
+          emptyDir: {}
+      restartPolicy: Always