Move the Unreleased fixes into 0.2.39, dated 2026-09-17, add the full-diff
link, and set KPlugin.Version to the released version.

Documentation impact: CHANGELOG.md only; no guide or TODO entry changes,
since the release contains no new behavior beyond the shipped fixes.

Verified with make check (exit 0), make package, and
python3 scripts/changelog.py --tag v0.2.39.

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>