Tier III: Last Glacial Maximum (lgm) evaluation

## Description
Evaluate model against LGM (~21 ka) proxy reconstructions. Strongest constraint on ECS upper bound.

## Specification
- PMIP4 protocol: expanded ice sheets, CO2 ~190 ppm
- Spatial temperature pattern comparison
- CRPS-based scoring with proxy uncertainties

## Proxy datasets
Tierney et al. (2020), Osman et al. (2021), Bartlein et al. (2011)

## Required simulations
lgm (≥500 years, equilibrium)

## References
Zhu et al., 2022 (CESM2 LGM constraints)