Add new lecture: Aiyagari model with Endogenous Grid Method

This PR adds a new lecture aiyagari_egm.md that combines the Aiyagari model with the Endogenous Grid Method (EGM).

Key Features:
- Combines concepts from egm_policy_iter.md and aiyagari.md
- Uses EGM to solve the household problem (avoiding costly root-finding)
- Uses simulation to compute aggregate capital (instead of analytical stationary distribution)
- EGM operator for the Aiyagari model - Corrected implementation, converges in ~90 iterations
- Simulation-based aggregation - Simulates 10,000+ households via Monte Carlo
- Equilibrium computation - Uses bisection to find equilibrium capital stock (K* ≈ 8)
- Wealth distribution analysis - Histograms, Lorenz curves, and Gini coefficient
- Educational content - Comparison with standard approach and four exercises

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

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

Author: jstac

lectures/_toc.yml

@@ -107,6 +107,7 @@ parts:
   - file: markov_perf
   - file: uncertainty_traps
   - file: aiyagari
+  - file: aiyagari_egm
   - file: ak_aiyagari
 - caption: Asset Pricing and Finance
   numbered: true