Finalize alpha release documentation

[DelshadH]

Summary

• replace prospective and authentication-unavailable release notes with the exact published npm state
• document the explicit alpha install command and registry-assigned initial latest tag
• date the changelog release entry
• update release-document regression tests

Verification

• npm run check: 158 passed
• git diff --check: passed

This changes documentation only. It does not republish packages, move the immutable tag, or rerun the bootstrap workflow.

[DelshadH]

Independent AI review of exact head 7f0cd4c: APPROVE. No P0, P1, or P2 findings. One non-blocking P3 noted that the documentation regression test could assert more of the already-correct prose. Reviewer independently verified the immutable tag commit, all four live package versions, registry signatures, provenance metadata, alpha/latest tags, and preserved observation-authenticity warning. This records AI review, not human approval.