Pin the delete handler's blocking closure result type

The closure's early returns go through `?`; naming its Ok error type keeps
inference from depending on the handler's tail expression.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Signed-off-by: CodeWhale Bot <[email protected]>

crates/tui/src/runtime_api/sessions.rs

@@ -929,7 +929,7 @@ pub(super) async fn delete_session(
         if let Err(error) = state.runtime_threads.unbind_session_threads(&id) {
             tracing::warn!(session_id = %id, %error, "deleted session's threads were not unbound");
         }
-        Ok(StatusCode::NO_CONTENT)
+        Ok::<_, ApiError>(StatusCode::NO_CONTENT)
     })
     .await
     .map_err(|_| ApiError::internal("session delete failed"))?