release: publish attested ASTER package evidence

[tuzuminami]

Summary

• prepare a public tarball, checksum, CycloneDX SBOM, and in-toto provenance after an isolated consumer smoke test
• add a tag-only, split-permission release workflow that verifies main ancestry, attests artifacts, and refuses to replace a published release
• align package/runtime exports, OpenAPI metadata, docs, and v2.0.1 release notes

Closes #44

Verification

• pnpm run verify (39 pass, 4 PostgreSQL tests skipped because this machine has no Docker/database)
• pnpm audit --prod --audit-level=high
• pnpm run prepare:release-assets -- --output-dir ...
• shasum -a 256 -c SHA256SUMS
• workflow YAML parse

Security review

The build job remains read-only; only the post-build publication job receives release and attestation permissions. It rechecks that the tag still points at the verified main commit before publishing.