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/locales/en/tracking.json

@@ -1,5 +1,14 @@
 {
   "title": "Activity Tracking",
+  "trackActivity": "Track Activity",
+  "selectActivity": "Select an activity to track",
+  "activities": {
+    "feeding": "Feeding",
+    "sleep": "Sleep",
+    "diaper": "Diaper",
+    "medicine": "Medicine",
+    "activity": "Activity"
+  },
   "feeding": {
     "title": "Feeding",
     "addFeeding": "Add Feeding",