This PR adds automatic ProofWidgets4 version pin updates to
`release_steps.py` when processing mathlib4. ProofWidgets4 uses
sequential version tags (`v0.0.X`) rather than toolchain-based tags
(`v4.X.Y`), so the existing regex that updates dependency versions in
lakefiles doesn't match it. This has caused CI failures in two
consecutive releases where the mathlib4 PR was created with a stale
ProofWidgets4 pin.
Changes:
- `script/release_steps.py`: Add `find_proofwidgets_tag()` to look up
the latest ProofWidgets4 tag compatible with the target toolchain, and
use it to update mathlib4's lakefile automatically
- `doc/dev/release_checklist.md`: Document the ProofWidgets4 pin update
step for mathlib4
🤖 Prepared with Claude Code
---------
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
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