Add continuous distribution and volatility analysis to McCall model (#707)

This commit addresses issue #707 by extending the basic McCall model:

- Add "Continuous Offer Distribution" section
  - Move continuous wage distribution from exercises to main content
  - Implement lognormal wage distribution with Monte Carlo integration
  - Show how reservation wage varies with c and β using contour plots

- Add "Volatility" section
  - Demonstrate that reservation wage increases with volatility
  - Use mean-preserving spread with lognormal distribution
  - Illustrate how workers prefer more volatile distributions

- Update exercise mm_ex1 solution
  - Change from discrete to continuous distribution
  - Use JAX implementation with continuous wage draws

- Remove exercise mm_ex2 (now covered in main text)

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

Author: jstac