CHANGELOG.md: reflect that v0.1.0 is now tagged, not still Unreleased

The v0.1.0 tag was created in the same session right after this file was
written, leaving it self-inconsistent: a tagged v0.1.0 whose own
CHANGELOG.md still said "no version has been tagged yet" under an
[Unreleased] heading. Fixed by renaming the heading to "[0.1.0] -
2026-09-14" and updating the framing paragraph.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UqJpkdJ6Njnt1pw3CbghzB

CHANGELOG.md

@@ -7,12 +7,12 @@ project follows [Semantic Versioning](https://semver.org/); see
 version (`packfs.pc`, generated by `make install`, is derived from it, not
 maintained separately).
 
-No version has been tagged yet — this project is pre-release (`0.x`, an
-initial, partial implementation of `concept.md`, not a completed one; see
-`README.md`'s "Status"). Entries below are grouped as they will read once
-`0.1.0` is tagged.
+This project is pre-release (`0.x`, an initial, partial implementation of
+`concept.md`, not a completed one; see `README.md`'s "Status"). `v0.1.0` is
+tagged locally in this repository's own git history but has not been
+pushed to any remote — there is no public release yet, only a local one.
 
-## [Unreleased]
+## [0.1.0] - 2026-09-14
 
 ### Added
 - Initial implementation of `concept.md`: `vfs_*` core, `mem`/`dir`/`pack`
@@ -67,5 +67,5 @@ initial, partial implementation of `concept.md`, not a completed one; see
 
 <!-- This repository has no remote configured yet (see `git remote -v`),
      so there is no comparison-link URL to cite here truthfully; add
-     "[Unreleased]: <repo-url>/compare/v0.1.0...HEAD" once one exists and
-     v0.1.0 is tagged, per Keep a Changelog's own convention. -->
+     "[0.1.0]: <repo-url>/releases/tag/v0.1.0" once one exists, per Keep
+     a Changelog's own convention. -->