chore: add ok/service fields to readiness response for consistency

Matches the response shape used by all other services in the
infrastructure (ok, service, cause on failure).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tidal-server/src/router.rs

@@ -421,7 +421,8 @@ async fn health(
     Ok((
         StatusCode::OK,
         Json(serde_json::json!({
-            "status": "ok",
+            "ok": true,
+            "service": "tidaldb",
             "mode": "standalone",
             "items": items,
         })),