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/children.json

@@ -0,0 +1,29 @@
+{
+  "title": "Children",
+  "subtitle": "Manage your family's children profiles",
+  "addChild": "Add Child",
+  "addFirstChild": "Add First Child",
+  "editChild": "Edit Child",
+  "deleteChild": "Delete Child",
+  "noChildren": "No children added yet",
+  "noChildrenSubtitle": "Add your first child to start tracking their activities",
+  "age": "Age",
+  "gender": {
+    "male": "Male",
+    "female": "Female",
+    "other": "Other"
+  },
+  "errors": {
+    "noFamily": "No family found. Please complete onboarding first.",
+    "loadFailed": "Failed to load children",
+    "saveFailed": "Failed to save child",
+    "deleteFailed": "Failed to delete child",
+    "noFamilyId": "No family ID found"
+  },
+  "ageFormat": {
+    "year": "year",
+    "years": "years",
+    "month": "month",
+    "months": "months"
+  }
+}