CHANGELOG.md now tracks version history (0.1.0 baseline); progress.md and
implementation-plan.md keep only live process and unfinished work (open
questions, optional 2.x.x phase O1) since phases 0-11 are fully closed and
already covered by git history and the changelog.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
