Fix Modules 2 & 3 Structure

This will clean up duplicate topics and restructure Module 3 correctly.

Module 2 fixes:

🗑️ Remove any duplicate or misplaced "Powers and Roots" topics
✅ Keep only the correct one at order 10

Module 3 fixes:

🗑️ Delete all existing topics in Module 3
✅ Create: Prime Numbers (Topic 11)
✅ Create: Factors and Multiples (Topic 12)
✅ Create: Common Factors and Multiples (Topic 13)
✅ Create: Prime Factorisation (Topic 14)