Add LeetCode recommendation feature to job description

[ytLin27]

Summary

• Added LeetCode recommendation section below job description display
• Backend API now returns recommended LeetCode problems based on job requirements
• Frontend displays 3 recommended problems with difficulty badges and reasons

Changes

Backend

• Added leetcode_recommendations field to extract_skills API response
• Added missing django-filter dependency to requirements.txt

Frontend

• Display LeetCode recommendations below job description with:
  • Problem number and title (clickable link to LeetCode)
  • Difficulty badge (Easy/Medium/Hard with color coding)
  • Recommendation reason
• Added responsive styling for LeetCode cards
• Fixed code formatting with Prettier

Testing

• ✅ Lint check passed
• ✅ Prettier format check passed
• ✅ Backend API returns leetcode_recommendations field
• ✅ Frontend correctly displays recommendations

[yangzhijiany]

Approved