ci(ruff): pin ruff below 0.16 to match the pinned pre-commit hook

[tuyakhov]

What

CI installs the dev extra with a floating ruff>=0.5, so it now resolves to
ruff 0.16, which formats Python code blocks inside Markdown by default.
That makes the ruff format --check . gate reformat README.md and fail —
even though the pinned ruff-pre-commit hook (v0.15.17) and local runs are
clean. It's the reason the Lint & type-check job (and the aggregate CI
gate that depends on it) is currently red on this branch.

Fix

Pin ruff==0.15.17 in the dev extra so CI matches the already-pinned
pre-commit hook and the lint gate is deterministic. One line in
pyproject.toml; no source changes.

Verification

• ruff format --check . — clean under 0.15.17; reformats README.md under 0.16 (the failure this fixes).
• ruff check . — passes.

Targeted at this inbound branch so its CI goes green; the inbound follow-up PR
stacked on it inherits the fix.

Note: this pins CI to match the pre-commit rev. A future ruff bump should
move both .pre-commit-config.yaml and this pin together. Alternative, if you'd
rather stay on floating/latest ruff: add [tool.ruff.format] exclude = ["*.md"]
instead — happy to switch to that.

---

Generated by Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!