feat(participants): add profile links to usernames in Participants tab

Enabled profile links for all usernames in the event Participants sidebar.
Users can now click on any participant's username to view their public
profile page at /u/username.

This improves user discoverability and allows participants to learn more
about other dancers before connecting or sending match requests.

Changes:
- Set linkToProfile={true} in ParticipantsSidebar for all UserListItem components
- Usernames now display as clickable links with hover state

frontend/src/components/events/ParticipantsSidebar.jsx

@@ -92,6 +92,7 @@ const ParticipantsSidebar = ({
               heats={thisUserHeats}
               competitorNumber={competitorNumber}
               showHeats={true}
+              linkToProfile={true}
               actionButton={
                 <button
                   onClick={() => onMatchWith?.(displayUser.userId)}