[the1mills]

Stacks the current-main package-reader authentication from #123 with the canonical SHA visibility read from zed-lib-core#84.

Security behavior:

• resolves all bounded canonical package references for an artifact SHA before serving bytes;
• legacy-only digests retain the existing anonymous compatibility behavior;
• if any canonical reference is public, the shared bytes remain anonymous/public;
• if every canonical reference is private, requires the scoped Shared Auth CLI delegation from DEN-2859: salvage delegated CLI package-reader boundary #123;
• maps the delegated principal to the canonical registry user, then requires org membership or direct project membership in at least one referencing package;
• unauthorized private reads return 404 after authentication so membership failure does not confirm private artifact existence;
• download/redirect happens only after authorization;
• includes regression coverage for empty/public/shared-public/all-private digest policy.

This directly advances Zed backlog task 7 at the origin digest route. The Cloudflare capability/ACL path remains the next layer (#124 salvage).

[linear-code]

DEN-2859