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>
d9ef5ed79a