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/tracking.ts

@@ -0,0 +1,80 @@
+import apiClient from './client';
+
+export type ActivityType = 'feeding' | 'sleep' | 'diaper' | 'medication' | 'milestone' | 'note';
+
+export interface Activity {
+  id: string;
+  childId: string;
+  type: ActivityType;
+  timestamp: string;
+  data: any;
+  notes?: string;
+  loggedBy: string;
+  createdAt: string;
+}
+
+export interface CreateActivityData {
+  type: ActivityType;
+  timestamp: string;
+  data: any;
+  notes?: string;
+}
+
+export interface UpdateActivityData extends Partial<CreateActivityData> {}
+
+export interface DailySummary {
+  date: string;
+  feedingCount: number;
+  sleepTotalMinutes: number;
+  diaperCount: number;
+  activities: Activity[];
+}
+
+export const trackingApi = {
+  // Get all activities for a child
+  getActivities: async (
+    childId: string,
+    type?: ActivityType,
+    startDate?: string,
+    endDate?: string
+  ): Promise<Activity[]> => {
+    const params: any = { childId };
+    if (type) params.type = type;
+    if (startDate) params.startDate = startDate;
+    if (endDate) params.endDate = endDate;
+
+    const response = await apiClient.get('/api/v1/activities', { params });
+    return response.data.data.activities;
+  },
+
+  // Get a specific activity
+  getActivity: async (id: string): Promise<Activity> => {
+    const response = await apiClient.get(`/api/v1/activities/${id}`);
+    return response.data.data.activity;
+  },
+
+  // Create a new activity
+  createActivity: async (childId: string, data: CreateActivityData): Promise<Activity> => {
+    const response = await apiClient.post(`/api/v1/activities?childId=${childId}`, data);
+    return response.data.data.activity;
+  },
+
+  // Update an activity
+  updateActivity: async (id: string, data: UpdateActivityData): Promise<Activity> => {
+    const response = await apiClient.patch(`/api/v1/activities/${id}`, data);
+    return response.data.data.activity;
+  },
+
+  // Delete an activity
+  deleteActivity: async (id: string): Promise<void> => {
+    await apiClient.delete(`/api/v1/activities/${id}`);
+  },
+
+  // Get daily summary
+  getDailySummary: async (childId: string, date: string): Promise<DailySummary> => {
+    const response = await apiClient.get('/api/v1/activities/daily-summary', {
+      params: { childId, date },
+    });
+    return response.data.data;
+  },
+};