docs: record Registry Alpha release

[tensornull]

Summary

• mark the 0.1.0a1 Registry Alpha milestone complete
• link the immutable recovery release, successful release workflow, and exact PyPI release
• record tag, release commit, provenance, digest, install, import, and mocked-smoke evidence
• keep the pypi reviewer in GitHub environment configuration and keep Release Please disabled pending a reviewed last-release-sha bridge

Why

The functional alpha is now published and fully verified. Public documentation still described it as awaiting authorization or unpublished, so this evidence-only change aligns the repository contract with shipped state.

Validation

• uv sync --locked
• Ruff check and format check
• Pyright
• 205 non-live tests
• version, public-document, secret, workflow, and actionlint checks
• exact wheel/sdist build, Twine, artifact, clean-install, and copied-repository checks
• independent adversarial documentation review: no blocker
• read-only GitHub and PyPI verification of release/tag/run/environment/digests