Add new lecture: Job Search with Separation and Markov Wages

This commit adds a new lecture that extends the job search model with separation by introducing Markov wage offers instead of IID wage offers.

Key changes:
- Added mccall_model_with_sep_markov.md to the lectures directory
- Updated _toc.yml to include the new lecture after mccall_model_with_separation
- Formatted the lecture header to match the QuantEcon lecture style (myst format, reference label, QuantEcon header)
- Added introduction that clearly references the previous lecture and explains the key difference (Markov vs IID wage offers)
- Lecture includes full implementation using JAX, value function iteration, sensitivity analysis, and cross-sectional simulations

The new lecture demonstrates how wage persistence affects job search decisions and labor market dynamics.

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

Co-Authored-By: Claude <[email protected]>

Author: jstac

lectures/_toc.yml

@@ -65,6 +65,7 @@ parts:
   chapters:
   - file: mccall_model
   - file: mccall_model_with_separation
+  - file: mccall_model_with_sep_markov
   - file: mccall_fitted_vfi
   - file: mccall_correlated
   - file: career