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/vault-secrets.yaml

@@ -0,0 +1,39 @@
+---
+apiVersion: secrets.hashicorp.com/v1beta1
+kind: VaultAuth
+metadata:
+  name: vso-auth
+  namespace: matrix
+spec:
+  method: kubernetes
+  mount: kubernetes
+  kubernetes:
+    role: vso
+    serviceAccount: default
+---
+apiVersion: secrets.hashicorp.com/v1beta1
+kind: VaultStaticSecret
+metadata:
+  name: tuwunel-secrets
+  namespace: matrix
+spec:
+  vaultAuthRef: vso-auth
+  mount: secret
+  type: kv-v2
+  path: tuwunel
+  refreshAfter: 60s
+  destination:
+    name: tuwunel-secrets
+    create: true
+    overwrite: true
+    transformation:
+      excludeRaw: true
+      templates:
+        TUWUNEL_OIDC_CLIENT_ID:
+          text: "{{ index .Secrets \"oidc-client-id\" }}"
+        TUWUNEL_OIDC_CLIENT_SECRET:
+          text: "{{ index .Secrets \"oidc-client-secret\" }}"
+        TUWUNEL_TURN_SECRET:
+          text: "{{ index .Secrets \"turn-secret\" }}"
+        TUWUNEL_REGISTRATION_TOKEN:
+          text: "{{ index .Secrets \"registration-token\" }}"