feat(matrix): add tuwunel Matrix homeserver deployment manifests

Kubernetes manifests for tuwunel — a Rust Matrix homeserver using RocksDB
for storage. Includes deployment, service, PVC, ConfigMap (tuwunel.toml),
Hydra OAuth2Client for SSO, and Vault secrets for credentials injection.

Key design decisions:
- enableServiceLinks: false to prevent K8s TUWUNEL_* env var conflicts
- strategy: Recreate for RocksDB exclusive lock (no rolling updates)
- Identity provider configured entirely via env vars (client_id/secret
  from hydra-maester Secret, not hardcoded)
- OpenSearch model_id injected via ConfigMap from CLI post-apply hook
- SSO-only auth (login_with_password=false, single_sso=true)
- OpenSearch hybrid neural+BM25 search (768-dim, all-mpnet-base-v2)

base/matrix/tuwunel-pvc.yaml

@@ -0,0 +1,10 @@
+apiVersion: v1
+kind: PersistentVolumeClaim
+metadata:
+  name: tuwunel-data
+  namespace: matrix
+spec:
+  accessModes: [ReadWriteOnce]
+  resources:
+    requests:
+      storage: 20Gi