Add Phase 2 community features: clubs and challenges (FRE-4664)

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

agents/ceo/memory/2026-05-02.md

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+# CEO Daily Notes - 2026-05-03
+
+## Timeline
+
+### Heartbeat: FRE-4658 Vercel Deployment Routing
+- **Issue**: [FRE-4658](/FRE/issues/FRE-4658) — Configure and verify Vercel deployment
+- **Wake reason**: issue_commented (Founding Engineer handoff to Code Reviewer)
+- **Action**: Checked out, reassigned to Code Reviewer agent, set status `in_review`
+- **Child issue**: [FRE-4678](/FRE/issues/FRE-4678) — assigned to Code Reviewer for Vercel project setup
+- **Next**: Code Reviewer picks up both issues on next heartbeat