feat: Apply localization to Track and Children pages (Phase 9 - Batch 2)

**Pages Localized:**
- Track main page: Activity selection menu with all tracking options
- Children page: Complete localization including age formatting with pluralization

**Translation Files:**
- Enhanced tracking.json: Added trackActivity, selectActivity, and activities keys
- Created children.json for all 5 languages with comprehensive strings
- Updated i18n config to include children namespace

**Key Features:**
- Localized age calculation with proper pluralization (year/years, month/months)
- All error messages translated
- Gender labels localized
- Properly formatted age display for all languages

**Languages Supported:**
- English, Spanish, French, Portuguese, Chinese (Simplified)

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

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

maternal-web/app/track/page.tsx

@@ -5,37 +5,39 @@ import { Restaurant, Hotel, BabyChangingStation, ChildCare, MedicalServices } fr
 import { useRouter } from 'next/navigation';
 import { AppShell } from '@/components/layouts/AppShell/AppShell';
 import { ProtectedRoute } from '@/components/common/ProtectedRoute';
+import { useTranslation } from '@/hooks/useTranslation';
 
 export default function TrackPage() {
+  const { t } = useTranslation('tracking');
   const router = useRouter();
 
   const trackingOptions = [
     {
-      title: 'Feeding',
+      title: t('activities.feeding'),
       icon: <Restaurant sx={{ fontSize: 48, color: 'primary.main' }} />,
       path: '/track/feeding',
       color: '#FFE4E1',
     },
     {
-      title: 'Sleep',
+      title: t('activities.sleep'),
       icon: <Hotel sx={{ fontSize: 48, color: 'info.main' }} />,
       path: '/track/sleep',
       color: '#E1F5FF',
     },
     {
-      title: 'Diaper',
+      title: t('activities.diaper'),
       icon: <BabyChangingStation sx={{ fontSize: 48, color: 'warning.main' }} />,
       path: '/track/diaper',
       color: '#FFF4E1',
     },
     {
-      title: 'Medicine',
+      title: t('activities.medicine'),
       icon: <MedicalServices sx={{ fontSize: 48, color: 'error.main' }} />,
       path: '/track/medicine',
       color: '#FFE8E8',
     },
     {
-      title: 'Activity',
+      title: t('activities.activity'),
       icon: <ChildCare sx={{ fontSize: 48, color: 'success.main' }} />,
       path: '/track/activity',
       color: '#E8F5E9',
@@ -47,10 +49,10 @@ export default function TrackPage() {
       <AppShell>
         <Box>
           <Typography variant="h4" fontWeight="600" gutterBottom>
-            Track Activity
+            {t('trackActivity')}
           </Typography>
           <Typography variant="body1" color="text.secondary" sx={{ mb: 4 }}>
-            Select an activity to track
+            {t('selectActivity')}
           </Typography>
 
           <Grid container spacing={3}>