perf(editor): Extract memoized list item components to prevent callback recreation

Summary

Extract list items into memoized sub-components with useCallback handlers to prevent unnecessary re-renders from inline callback creation.

Background

Identified in PR #196 review: https://github.com/aafre/resume-builder/pull/196#discussion_r2674280330

Inline callbacks in .map() loops create new function instances on every render, causing child components to re-render unnecessarily.

Affected Files

• ExperienceSection.tsx - Lines 131, 187, 198, 210, 230, 259 (most critical - nested loops)
• EducationSection.tsx - Lines 165, 185, 199, 210, 223, 234
• GenericSection.tsx - Lines 130, 149, 155, 190, 209, 215, 250, 269, 275
• IconListSection.tsx - Lines 144, 165, 181, 194, 205, 213
• ContactInfoSection.tsx - Lines 152, 176, 206, 229

Approach

1. Create memoized sub-components:

   • DescriptionItem for experience descriptions
   • ExperienceEntry for experience cards
   • EducationEntry for education cards
   • ListItem variants for GenericSection
   • CertificationItem for IconListSection
   • SocialLinkItem for ContactInfoSection

2. Use React.memo() wrapper on sub-components

3. Use useCallback for handlers inside sub-components

4. Pass stable callbacks from parent (memoized with useCallback)

Example Pattern

// Before
{items.map((item, index) => (
  <RichTextInput onChange={(value) => handleUpdate(index, value)} />
))}

// After
const MemoizedItem = React.memo(({ index, onUpdate }) => {
  const handleChange = useCallback((value) => onUpdate(index, value), [index, onUpdate]);
  return <RichTextInput onChange={handleChange} />;
});

Priority

Medium - Performance optimization. Most impactful for resumes with many experience entries and description points.