Following the 216dcab fix that added [FromBody] BaseRequest _ to the
Info action, the existing tests' empty new {} payloads no longer satisfy
[ApiController] model validation (BaseRequest.ViewerId is non-nullable
string). Use the same EmptyBody() shape as RankBattleControllerTests
to mirror the production wire.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>