Move the Unreleased entries into 0.2.43, dated 2026-09-27, add the full-diff link, and set KPlugin.Version to the released version.

Documentation impact: CHANGELOG.md moves already-reviewed Unreleased entries (verified against the v0.2.42..HEAD scope) into the versioned section. No guide or TODO changes: the release ships the behavior those guides already describe; TODO baseline remains upstream 0.67.0 with 0.68.0 pending its own review.