Implement full MVVM stack for two new community features:
Clubs:
- Persistent runner groups with type, privacy, and member management
- Club discovery, creation, join/leave, and invite workflows
- Member roles (Owner, Admin, Member) and capacity limits
Challenges:
- Time-bound competitive goals with progress tracking and leaderboards
- Challenge types: distance, time, frequency, elevation, calories, streak
- Progress submission, participation status, and ranking
Files:
- Models: Club.swift, Challenge.swift
- Services: ClubService.swift, ChallengeService.swift
- ViewModels: ClubViewModel.swift, ChallengeViewModel.swift
- Views: ClubsView.swift, ClubDetailView.swift, ChallengesView.swift, ChallengeDetailView.swift
- Tests: ClubServiceTests.swift, ChallengeServiceTests.swift
- Updated README.md with new feature documentation
88d57a3389