Add Sud.derive_plant_params(), which combines pot_mass/pot_material/ grain_mass/water_mass into a single lumped (mass, specific heat) pair using approximate specific-heat constants for water, grain, and (by a small material lookup table) the pot itself. demo_sud.py now builds its plant_params from this instead of hardcoded C/M values, keeping L/Td as the only manually-tuned plant parameters. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>