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/hydra-oauth2client.yaml

@@ -0,0 +1,22 @@
+# Tuwunel OIDC client — registered with Hydra via hydra-maester.
+# Hydra Maester creates K8s Secret "oidc-tuwunel" in the matrix namespace
+# with CLIENT_ID and CLIENT_SECRET keys.
+# redirectUri is patched post-apply by sunbeam CLI (requires client_id
+# from the hydra-maester-generated secret).
+apiVersion: hydra.ory.sh/v1alpha1
+kind: OAuth2Client
+metadata:
+  name: tuwunel
+  namespace: matrix
+spec:
+  clientName: Matrix
+  grantTypes:
+    - authorization_code
+    - refresh_token
+  responseTypes:
+    - code
+  scope: openid email profile
+  redirectUris: []
+  tokenEndpointAuthMethod: client_secret_post
+  secretName: oidc-tuwunel
+  skipConsent: true