docs(changelog): log the Apache-2.0 license restore

[sotberd]

Summary

Follow-up to #9, which restored LICENSE to the verbatim Apache-2.0 text but merged without a CHANGELOG.md entry.

This repo does log repo-wide governance changes — [Unreleased] already carries the CLA-to-DCO switch and the NOTICE addition from #4, both unprefixed since they aren't plugin-scoped. The license restore belongs beside them, otherwise the section reads as incomplete when the next release notes are written.

Changelog-only. No plugin, workflow, or license file is touched.

Type of change

• Bug fix (non-breaking)
• New feature (non-breaking)
• Breaking change (would alter existing slash-command behavior or config schema)
• New plugin
• Documentation only
• Build / tooling / CI

Tested in

• Claude Code (version: _____) — n/a, no plugin code or manifest changed
• Cursor (version: _____) — n/a, same

Checklist

• Plugin tests pass (./tests/run-tests.sh inside the affected plugin) — n/a, no plugin affected; nothing under plugins/ is touched
• Interactive flow verified manually in both Claude Code and Cursor — n/a, no interactive flow changed
• CHANGELOG.md updated under [Unreleased] with plugin name prefix — this PR is that entry; logged unprefixed under ### Changed, matching the other repo-wide entries
• All commits are signed off (git commit -s) — see DCO.md

Linked issue(s)