bug: respect admin mode for expired tournament check-ins

[zeeshaun]

Fixes 5stackgg/5stack-panel#429

[lukepolo]

Thanks @zeeshaun — re-landed this as #280 since this branch is on your fork and I wanted to push the review fixups directly. Your commit is preserved as-is (you're the author on it), with my changes layered on top:

• Linked the MatchSupport notification to the match + red color (it was a bare match ID before), matching our existing match-support convention.
• Added an explicit de-dupe so we don't re-notify when an unread MatchSupport already exists, rather than relying solely on nulling cancels_at.
• Documented the auto-mode coin-toss, and confirmed byes can't reach this path (they resolve at the bracket level before a match row exists).

Closing in favor of #280. Appreciate the fix! 🙏