Fix admin username underscore

[Ishta-P-Jain]

Summary

MediaWiki treats underscores and spaces in usernames as
interchangeable, but wscontest was comparing them as plain strings
in several places:

• ContestsController::edit() and ::delete() compared admin names
  with strict ===.
• ContestRepository::hasAdmin() (which controls whether the Edit
  button is shown at all) used an exact LIKE match in SQL.
• ContestsController::save() stored whatever raw string was typed
  into the admins textarea, underscore and all.

This PR normalizes underscores to spaces on both sides of every
admin-username comparison, and normalizes admin names before they're
saved, so the two forms of a username are always treated as
equivalent.

Testing

Manually verified locally that:

• Adding an admin with an underscored username and saving no longer
  breaks their ability to edit the contest.
• Existing admins added before this fix (with underscores already in
  the database) can now also edit, thanks to the hasAdmin() fix.

Bug: T336157

[samwilson]

Looks good. A few suggestions. Also, there are some CI issues.

[Ishta-P-Jain]

Thanks for the review! I've addressed the suggested changes. I noticed the remaining CI failure is in IndexPageRepositoryTest with a 403 Forbidden response from the Wikidata Query Service. Is this an existing CI issue, or would you like me to investigate it further?
let me know if there's anything else that should be updated

[samwilson]

Thanks! Looks good.

I'm attempting to fix the CI failure: wikisource/api#19