fix· GitHub
GitHub requests explain access refusals
Eligible requests on known Sinatra PRs now receive a sign-in link when workspace access cannot be verified.
We leave the agent idle until the requester's GitHub identity and workspace membership pass the existing check. The public reply is the same for an unknown account and a known non-member; account-specific recovery stays behind sign-in. Passive reviews and unrelated comments stay silent, and repeating the same refused request uses the existing short comment-deduplication window.
#1499