Add visualization and convergence demonstration to fitted VFI lecture

- Add vertical black line to plot showing reservation wage w_bar
- Fix markdown formatting issue with empty code cell
- Add demonstration showing how increasing simulation length (T=10,000) reduces difference between time-average and cross-sectional unemployment rates from 0.0594 to 0.0016
- Reorganize sections for better flow and clarity
- Improve code structure and documentation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: jstac