RequireUnitReader now checks for LicensedReadOnly context flag
before checking standard permissions. This lets the releases
download route pass through for licensed private repos where
RepoAssignment granted read-only access via license key.
Fixes the 404 on /releases/download/ with valid dlid= param.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>