v0.7.21

Removed — the Claude artifact

• src/epochix/_artifacts/epochix.artifact.jsx is withdrawn, with its
  README section. It was a third, hand-written engine last touched in 0.3.0:
  it graded regression and generative runs on perplexity bands, had no notion
  of a metric's direction, and animated neuron "activations" from
  Math.random(). Anyone following the README could get a different grade
  from the product for the same log. Rebuilding it would mean generating it
  from the Python engine's tables, as the VS Code extension's engine is now.

Fixed — what a visitor meets outside the code

• Every GitHub release had an empty body — all 136. The "Latest" link on
  the repository opened a page with files and no words. All are now filled
  from their CHANGELOG sections (five early ones that never had a section say
  so), and the release workflow publishes the version's section as its notes
  from now on — scripts/release_notes.py, failing the release if the
  section is missing.
• Three README links were broken on PyPI (the licence, CONTRIBUTING and
  the demo's source), because PyPI resolves relative links against pypi.org.
  They are absolute now.
• A link to epochix.dev unfurled as a bare title on LinkedIn, Slack or X:
  the docs site had no link-preview tags. Every page now carries Open Graph
  and Twitter tags with a preview image.
• The social preview image was cropped mid-sentence and half empty. It is
  regenerated from the real dashboard on the real Keras demo run
  (asset/epochix_social.png, 1280x640 at 2x).
• Added a CODE_OF_CONDUCT.md (the Contributor Covenant 2.1, by reference,
  with a private reporting route) and a pull-request template carrying the
  project's gate.