Move the Unreleased entries into 0.2.42, dated 2026-09-25, 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 v0.2.41..HEAD scope) into the versioned section. The popup tab-button note is trimmed to its observable result. No guide or TODO changes: the release ships the behavior those guides already describe; upstream latest remains 0.66.0, already reviewed.