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/founding-engineer/life/projects/lendair-ios/items.yaml

@@ -0,0 +1,37 @@
+# Atomic facts for Lendair iOS project
+
+- id: "lendair-ios-fre4686"
+  type: "project_milestone"
+  date: "2026-05-03"
+  title: "Notifications screen implementation"
+  status: "in_progress"
+  details:
+    parent_issue: "FRE-4686"
+    child_issues:
+      - "FRE-4737"
+      - "FRE-4738"
+      - "FRE-4739"
+      - "FRE-4740"
+    implementation_approach: "MVVM with SwiftUI"
+    notification_types:
+      - "LOAN_APPROVED"
+      - "LOAN_REJECTED"
+      - "PAYMENT_RECEIVED"
+      - "PAYMENT_DUE"
+      - "NEW_LENDER"
+      - "SYSTEM_UPDATE"
+    files_created:
+      - "Lendair/Views/NotificationsView.swift"
+      - "Lendair/Views/NotificationRowView.swift"
+      - "Lendair/ViewModels/NotificationsViewModel.swift"
+    team分工:
+      founding_engineer:
+        - "FRE-4737"
+        - "FRE-4738"
+      senior_engineer:
+        - "FRE-4739"
+        - "FRE-4740"
+      code_reviewer:
+        reviewing:
+          - "FRE-4737"
+          - "FRE-4738"