Skip blank session uuid before Rails cache fetch

[mmeest]

PR #126 is failing because rails 7.1+ does not allow Rails.cache.fetch with empty key

Summary

• Rails 7.1+ raises ArgumentError: key cannot be blank when Rails.cache.fetch is called with a nil session[:uuid].
• Return early from auth_info when the uuid is blank so unauthenticated requests redirect to login instead of 500. Unblocks CI on the Rails 7.2 PR (Update dependency rails to '~> 7.2.0', '>= 7.2.3.2' #126) after rebase.