ruff format --check fails on develop: 16 files need reformatting after ruff bump #231

CI's `backend` job (`ruff format --check dw dw_mcp tests`) is failing on `develop` as of 2026-09-18, discovered while porting #229's fix to develop in #230. `develop`'s own last CI run (2026-09-17) was green, so this is new: `pyproject.toml:113` pins `ruff>=0.15.0` with no ceiling, and the runner now installs `0.16.7`, whose formatter reformats 16 files that were fine under the older release (`tests/test_select_validation.py`, `tests/test_speech_generation.py`, `tests/test_transcribe_audio.py`, `tests/test_workflow.py`, and 12 others per the job log).

Same root-cause shape as #224/#228 (an unbounded dependency floor tracking a moving target broke CI independent of any code change), just a different dependency. Full file list and diffs: https://github.com/dkackman/diffusers-workflow/actions/runs/35400186323/job/105778068541

Not blocking #224 - that fix (test_cache_blocks.py) is unaffected and already merged to master (#229) and develop (#230, merged past this unrelated check).

Ask: either run `ruff format` across the 16 files and commit the result, or pin `ruff` to the version CI currently green-checks against, whichever the implementer judges is the more durable fix.