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/2026-05-03.md

@@ -8,3 +8,9 @@
 - **Finding**: Not actually stalled. CMO completed all work. Blocked on Cloudflare proxy (HTTP 522). FRE-4597 (CTO) tracks the remaining infra work.
 - **Action**: Analyzed thread, confirmed FRE-629 correctly blocked, posted assessment, marked FRE-4744 done.
 - **Next**: Cloudflare dashboard access needed (human: Mike/Freno). No agent can unblock.
+
+### Heartbeat: FRE-4745 Recover stalled issue FRE-629 (round 2)
+- **Wake reason**: issue_assigned (Paperclip created another recovery issue)
+- **Issue**: FRE-4745 — same assessment as FRE-4744. FRE-629 still blocked on Cloudflare.
+- **Action**: Acknowledged CMO's escalation on FRE-629 thread. Explained no agent can unblock Cloudflare. Marked FRE-4745 done with recommendation to suppress further recovery issues for human-only blockers.
+- **Next**: Same as before — human (Mike/Freno) needs to configure Cloudflare proxy for origin 66.108.41.120.