release: v0.1.0

First cut release. Snapshots ./src/ as ./versions/v0.1.0/ via
`just cut-version v0.1.0` (22 files: 21 chapter MDs + SUMMARY.md).
Deployed alongside `latest` at:

  https://swaits.github.io/meshcore-spec/v0.1.0/

Also:

- CHANGELOG.md adopts Keep a Changelog-style version sections.
  Future entries land under [Unreleased] and graduate to a version
  heading when cut. The existing date-stamped pass entries stay
  put as a historical record of the work captured in v0.1.0.
- README.md fixes a stale "per vX.Y.Z tag" mention left over from
  the tag-based versioning model, and links the current release
  explicitly.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -1,5 +1,24 @@
 # Changelog
 
+This project follows a loose [Keep a Changelog](https://keepachangelog.com/en/1.1.0/)
+convention. Released versions live as frozen snapshots under `versions/vX.Y.Z/`
+in the repo; the rolling tip of `main` is what `latest` deploys.
+
+## [Unreleased]
+
+_(nothing yet)_
+
+## [v0.1.0] — 2026-05-12
+
+First cut release of the spec. Snapshotted as `versions/v0.1.0/`, deployed
+at <https://swaits.github.io/meshcore-spec/v0.1.0/>.
+
+The dated entries below describe the substantive passes whose output is
+captured in this release. Future releases will follow the standard
+Added / Changed / Fixed / Removed grouping under their version heading.
+
+---
+
 ## 2026-05-12 — Publication-Readiness Pass
 
 **Upstream baseline:** Validated against