Add backend API integration for Children, Family, and Tracking

API Services Created:
- lib/api/children.ts: Full CRUD operations for children management
- lib/api/families.ts: Family member management and invitations
- lib/api/tracking.ts: Activity tracking (feeding, sleep, diaper, etc.)

Children Page Implementation:
- Fetch and display children from backend API
- Add/Edit child with modal dialog (ChildDialog component)
- Delete child with confirmation (DeleteConfirmDialog component)
- Age calculation from birthDate
- Loading states and error handling
- Responsive card grid layout
- Gender-based avatar colors
- Empty state for no children

AuthContext Updates:
- Added families array to User interface
- Includes familyId for API calls

Components:
- components/children/ChildDialog.tsx: Form for add/edit child
- components/children/DeleteConfirmDialog.tsx: Delete confirmation

All components use Material-UI theme and include proper TypeScript types

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

maternal-web/lib/auth/AuthContext.tsx

@@ -10,6 +10,11 @@ export interface User {
   email: string;
   name: string;
   role: string;
+  families?: Array<{
+    id: string;
+    familyId: string;
+    role: string;
+  }>;
 }
 
 export interface LoginCredentials {