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/api/children.ts

@@ -0,0 +1,60 @@
+import apiClient from './client';
+
+export interface Child {
+  id: string;
+  familyId: string;
+  name: string;
+  birthDate: string;
+  gender: 'male' | 'female' | 'other';
+  photoUrl?: string;
+  medicalInfo?: any;
+  createdAt: string;
+}
+
+export interface CreateChildData {
+  name: string;
+  birthDate: string;
+  gender: 'male' | 'female' | 'other';
+  photoUrl?: string;
+  medicalInfo?: any;
+}
+
+export interface UpdateChildData extends Partial<CreateChildData> {}
+
+export const childrenApi = {
+  // Get all children for the authenticated user
+  getChildren: async (familyId?: string): Promise<Child[]> => {
+    const params = familyId ? { familyId } : {};
+    const response = await apiClient.get('/api/v1/children', { params });
+    return response.data.data.children;
+  },
+
+  // Get a specific child
+  getChild: async (id: string): Promise<Child> => {
+    const response = await apiClient.get(`/api/v1/children/${id}`);
+    return response.data.data.child;
+  },
+
+  // Create a new child
+  createChild: async (familyId: string, data: CreateChildData): Promise<Child> => {
+    const response = await apiClient.post(`/api/v1/children?familyId=${familyId}`, data);
+    return response.data.data.child;
+  },
+
+  // Update a child
+  updateChild: async (id: string, data: UpdateChildData): Promise<Child> => {
+    const response = await apiClient.patch(`/api/v1/children/${id}`, data);
+    return response.data.data.child;
+  },
+
+  // Delete a child
+  deleteChild: async (id: string): Promise<void> => {
+    await apiClient.delete(`/api/v1/children/${id}`);
+  },
+
+  // Get child's age
+  getChildAge: async (id: string): Promise<{ ageInMonths: number; ageInYears: number; remainingMonths: number }> => {
+    const response = await apiClient.get(`/api/v1/children/${id}/age`);
+    return response.data.data;
+  },
+};