Keep only comprehensive notebook, remove redundant files

The aei_rebate_analysis.ipynb notebook now contains all functionality:
- Reform definition and variables
- Household and tax unit calculations
- Official statistics validation
- Example calculations
- Clean tables and visualizations

Removed redundant files:
- aei_rebate.py (code now in notebook)
- test_*.py files (examples now in notebook)
- aei_rebate.ipynb (old draft notebook)

Author: MaxGhenis