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/zh/children.json

@@ -0,0 +1,29 @@
+{
+  "title": "儿童",
+  "subtitle": "管理您家庭的儿童档案",
+  "addChild": "添加儿童",
+  "addFirstChild": "添加第一个儿童",
+  "editChild": "编辑儿童",
+  "deleteChild": "删除儿童",
+  "noChildren": "还没有添加儿童",
+  "noChildrenSubtitle": "添加您的第一个儿童以开始追踪他们的活动",
+  "age": "年龄",
+  "gender": {
+    "male": "男",
+    "female": "女",
+    "other": "其他"
+  },
+  "errors": {
+    "noFamily": "未找到家庭。请先完成入职流程。",
+    "loadFailed": "加载儿童失败",
+    "saveFailed": "保存儿童失败",
+    "deleteFailed": "删除儿童失败",
+    "noFamilyId": "未找到家庭ID"
+  },
+  "ageFormat": {
+    "year": "年",
+    "years": "年",
+    "month": "个月",
+    "months": "个月"
+  }
+}

maternal-web/locales/zh/tracking.json

@@ -1,5 +1,14 @@
 {
-  "title": "Activity Tracking",
+  "title": "活动追踪",
+  "trackActivity": "记录活动",
+  "selectActivity": "选择要追踪的活动",
+  "activities": {
+    "feeding": "喂养",
+    "sleep": "睡眠",
+    "diaper": "尿布",
+    "medicine": "药物",
+    "activity": "活动"
+  },
   "feeding": {
     "title": "Feeding",
     "addFeeding": "Add Feeding",