#1094: return canonical full_name casing from Fbe.unmask_repos

[morphqdd]

A mask with no asterisk was pushed into the result verbatim, while a wildcard match used the full_name GitHub reported. The archived filter fetched the repository but discarded the canonical name it got back.

This meant the same repository could reach judges under different names depending on how it was matched, and Fbe.octo.repo_name_by_id (which always downcases) would then compare unequal to a name that came from a mask.

Now the exact-mask branch fetches the repository and uses its full_name, falling back to the mask string only if the fetch fails or the response has no full_name. The archived-status check also reuses the canonical full_name it already fetches instead of throwing it away.

Added a test with a mixed-case exact mask and an overlapping wildcard mask on the same repo, asserting one canonical spelling wins.

Closes #1094