ci: pin ruff so check-format stops failing on main

[BILLKISHORE]

What

make check-format fails on a clean main, so the lint job is red on new PRs. From the run on #2680:

uv run ruff format --check .
unformatted: File would be reformatted
5 files would be reformatted, 291 files already formatted
make: *** [Makefile:101: check-format] Error 1

No commit caused this. install-tools runs uv tool install ruff unpinned, and ruff 0.16 promoted markdown code-block formatting out of preview. CI picked up the new default on its next run, and five docs files that predate it started failing.

Bisecting the tool rather than the tree:

ruff	markdown formatting	check-format on clean main
0.14.0	preview only	pass
0.15.0	preview only	pass
0.16.1	on by default	fail

Fix

Two commits:

1. ruff format over the five affected files (README.md, the three package READMEs, libs/giskard-llm/docs/design.md). Formatting only: line wrapping, blank lines between top-level defs, quote normalisation, trailing commas. No prose or code semantics changed.
2. Pin RUFF_VERSION := 0.16.1 in install-tools, so the next ruff release can't turn make check red on a tree nobody touched. Same reasoning as the existing LICENSECHECK_VERSION pin.

I did consider pinning to 0.15 instead, which also makes main green with a one-line diff since 0.15 ignores markdown entirely. Freezing the toolchain to avoid a formatting change you'll take eventually didn't seem like the right call, especially as the same reformat is already riding along in a number of open PRs.

Testing

make check exits 0 on this branch and fails on main. make test-unit: 37 / 211 / 117 / 757 / 155 passed across core, llm, agents, checks and scan.

Note

The docs reformat already appears as a side effect in several open PRs (#2658 among them, byte-identical to this one). Landing it standalone lets those diffs shrink to just their real changes.

Type of Change

• 🥂 Improvement (non-breaking change which improves an existing feature)

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Disclosure: drafted with AI assistance (Claude Code). I reproduced the failure, bisected the ruff versions, and ran the checks myself before submitting.

[kevinmessiaen]

Thanks for fixing the CI !