Add visualization and convergence demonstration to fitted VFI lecture

[jstac]

Summary

This PR enhances the fitted value function iteration (VFI) lecture with improved visualizations and a demonstration of ergodic convergence properties.

Key Changes

1. Reservation Wage Visualization

   • Added vertical black line to the value function plot (line 453-454) to clearly mark the reservation wage w_bar
   • The line appears as a dashed black line with label showing on the legend for easy identification of where employment and continuation value functions intersect

2. Convergence Demonstration

   • Added new section demonstrating how the difference between time-average and cross-sectional unemployment rates decreases with longer simulations
   • Shows that with T=2,000: difference is 0.0594
   • Shows that with T=10,000: difference reduces to 0.0016 (~97% reduction)
   • This illustrates the ergodic property: long-run behavior of a single agent mirrors aggregate cross-sectional behavior

3. Code Quality Improvements

   • Fixed markdown formatting issue (removed empty code cell that was causing syntax errors)
   • Improved code organization and flow
   • Enhanced documentation and comments

4. Testing

   • Verified all code runs successfully using jupytext conversion
   • All plots generate correctly
   • All numerical outputs are consistent

Test Plan

• Convert markdown to Python using jupytext
• Run Python script successfully
• Verify reservation wage visualization appears correctly
• Verify convergence demonstration shows expected results
• Confirm no syntax or runtime errors

🤖 Generated with Claude Code

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📚 Changed Lecture Pages: mccall_fitted_vfi, mccall_model