Add install-test stage to the PR pipeline (k3d)

New install-test job in validate-charts.yml: for exactly the charts a PR
changes, install them into an ephemeral k3d cluster (pinned k3d v5.9.0,
k3s v1.35.5-k3s1) and require every Deployment/StatefulSet to become
Ready. Runs non-blocking (continue-on-error) during the stabilization
phase.

Fixtures live at the repo root under ci/ (not inside chart directories,
so they neither trigger publishes on merge nor get packaged): a stub
OnePasswordItem CRD, per-chart test values and fixtures (dummy secrets
with in-cluster DSNs, throwaway postgres/redis/dex, synapse-generate
seed job, static hostPath PVs where charts pin storage classes or need
RWX), plus a shared ci/run-install-test.sh harness that also runs
locally.

Excluded with documented reasons (ci/excluded-charts.txt): satisfactory
(multi-GB image), teamspeak-server (TS6 beta license expired, image
crashes on start), template-chart (placeholder image).

All 14 non-excluded charts verified locally in k3d using only the
committed fixtures.

ci/voucher-vault/fixtures.yaml

@@ -0,0 +1,188 @@
+# Fixtures for the voucher-vault install-test: throwaway postgres + redis
+# (Celery broker), a dex OIDC provider and the secrets the 1Password
+# operator would otherwise materialize (release name: ci).
+apiVersion: v1
+kind: Secret
+metadata:
+  name: ci-voucher-vault-secret
+stringData:
+  secretKey: voucher-vault-ci-django-secret-0123456789abcdef0123456789abcdef
+  redis-url: redis://:cipass@redis:6379/0
+---
+apiVersion: v1
+kind: Secret
+metadata:
+  name: ci-voucher-vault-db-secret
+stringData:
+  host: postgres
+  port: "5432"
+  user: ci
+  password: ci
+  database: vouchervault
+---
+apiVersion: v1
+kind: Secret
+metadata:
+  name: ci-voucher-vault-oidc-secret
+stringData:
+  oidc-jwks-endpoint: http://dex.default.svc.cluster.local:5556/dex/keys
+  client-id: ci-client
+  client-secret: ci-client-secret
+  authorization-endpoint: http://dex.default.svc.cluster.local:5556/dex/auth
+  token-endpoint: http://dex.default.svc.cluster.local:5556/dex/token
+  user-endpoint: http://dex.default.svc.cluster.local:5556/dex/userinfo
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: postgres
+  labels:
+    app: postgres
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      app: postgres
+  template:
+    metadata:
+      labels:
+        app: postgres
+    spec:
+      containers:
+        - name: postgres
+          image: public.ecr.aws/docker/library/postgres:16-alpine
+          env:
+            - name: POSTGRES_USER
+              value: ci
+            - name: POSTGRES_PASSWORD
+              value: ci
+            - name: POSTGRES_DB
+              value: vouchervault
+          ports:
+            - containerPort: 5432
+          readinessProbe:
+            exec:
+              command: ["pg_isready", "-U", "ci"]
+            periodSeconds: 5
+          volumeMounts:
+            - name: data
+              mountPath: /var/lib/postgresql/data
+      volumes:
+        - name: data
+          emptyDir: {}
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: postgres
+spec:
+  selector:
+    app: postgres
+  ports:
+    - port: 5432
+      targetPort: 5432
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: redis
+  labels:
+    app: redis
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      app: redis
+  template:
+    metadata:
+      labels:
+        app: redis
+    spec:
+      containers:
+        - name: redis
+          image: public.ecr.aws/docker/library/redis:7-alpine
+          args: ["redis-server", "--requirepass", "cipass"]
+          ports:
+            - containerPort: 6379
+          readinessProbe:
+            tcpSocket:
+              port: 6379
+            periodSeconds: 5
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: redis
+spec:
+  selector:
+    app: redis
+  ports:
+    - port: 6379
+      targetPort: 6379
+---
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: dex-config
+data:
+  config.yaml: |
+    issuer: http://dex.default.svc.cluster.local:5556/dex
+    storage:
+      type: memory
+    web:
+      http: 0.0.0.0:5556
+    oauth2:
+      skipApprovalScreen: true
+    staticClients:
+      - id: ci-client
+        secret: ci-client-secret
+        name: CI Client
+        redirectURIs:
+          - https://vv.ci.local/oidc/callback
+    enablePasswordDB: true
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: dex
+  labels:
+    app: dex
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      app: dex
+  template:
+    metadata:
+      labels:
+        app: dex
+    spec:
+      containers:
+        - name: dex
+          image: ghcr.io/dexidp/dex:v2.41.1
+          command: ["dex", "serve", "/etc/dex/cfg/config.yaml"]
+          ports:
+            - containerPort: 5556
+          readinessProbe:
+            httpGet:
+              path: /dex/healthz
+              port: 5556
+            periodSeconds: 5
+          volumeMounts:
+            - name: config
+              mountPath: /etc/dex/cfg
+      volumes:
+        - name: config
+          configMap:
+            name: dex-config
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: dex
+spec:
+  selector:
+    app: dex
+  ports:
+    - port: 5556
+      targetPort: 5556

ci/voucher-vault/test-values.yaml

@@ -0,0 +1,8 @@
+secrets:
+  voucherVaultSecretRef: op://ci/voucher-vault
+  oidcSecretRef: op://ci/voucher-vault-oidc
+  databaseSecretRef: op://ci/voucher-vault-db
+
+ingress:
+  clusterIssuer: ci
+  domain: vv.ci.local