Standardize continuation value notation in Job Search II lecture

Updated the McCall model with separation to use h = u(c) + β * sum_w v_u(w) q(w)
as the continuation value, matching the notation from the basic McCall model lecture.

This makes the progression between lectures more intuitive for readers:
- Basic model: h = c + β * sum_w v*(w) q(w)
- Separation model: h = u(c) + β * sum_w v_u(w) q(w)

Key changes:
- Replaced scalar d with h throughout mathematical derivations
- Updated closed-form expression for v_e(w) to use h
- Modified iteration algorithm to solve for h instead of d
- Simplified Bellman equations using h notation
- Updated all code functions (compute_v_e, update_h, solve_model)
- Changed plots and comments to reference h

This improves consistency across the job search lecture series and makes
the mathematical structure clearer by explicitly showing the continuation
value includes both current utility and discounted future value.

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

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

Author: jstac