* studio: drop unused max_grad_value schema + route plumbing
The MLX worker hardcodes max_grad_value to 5.0 after PR #5340. The
schema field, frontend payload type, route forwarder, and start_training
kwarg threading were all left in place as a transitional buffer for old
clients. The field is now genuinely unused everywhere except inside the
MLX worker, so the schema, route forwarder, and config-build entries can
go. Pydantic still tolerates older clients that send max_grad_value
because TrainingStartRequest's model_config defaults to extra=ignore.
* [pre-commit.ci] auto fixes from pre-commit.com hooks
for more information, see https://pre-commit.ci
---------
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
4192fe6ebe