WIP: Add challenges feature schema and operations

- Add Challenge, ChallengeEntry, ChallengeInvitation, RuleSet types
- Add queries: challenges, challenge, challengeLeaderboard, myChallengeInvitations, myChallengeEntries, ruleSets
- Add mutations: createChallenge, createRuleSet, inviteUsersToChallenge, respondToChallengeInvitation, startChallenge, submitChallengeEntry, recalculateChallengeEntry

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/operations/user.gql

@@ -163,3 +163,13 @@ fragment UserFragment on UserGQL {
   videosPrivateByDefault
   agreesToMarketing
 }
+
+query GetUsersMatching(
+  $matchString: String = null
+  $limit: Int = null
+  $after: String = null
+) {
+  getUsersMatching(matchString: $matchString, limit: $limit, after: $after) {
+    ...UserFragment
+  }
+}