fix(claude): use cleanup-tolerant temporary directory

[Yifan Yang (Yif-Yang)]

Summary

Immediate maintainer follow-up to #135, which was merged first with the contributor commit and attribution intact.

Python 3.10, the project minimum, already supports TemporaryDirectory(ignore_cleanup_errors=True). Use that standard lifecycle instead of manual mkdtemp plus rmtree(ignore_errors=True), while preserving the Windows WinError 32 tolerance introduced by #135.

The new platform-neutral regression test mocks a successful Claude result and simulates a Windows cleanup failure through TemporaryDirectory._rmtree. It verifies cleanup receives ignore_errors=True, the model result is preserved, and the temporary directory is removed.

Validation

• Focused regression: 1 passed
• pytest tests/ -q: 276 passed, 6 skipped
• git diff --check: clean
• Claude Code / Opus 4.8 read-only review: no blockers, MERGE