Bump the engine submodule to f791ee6 (Calendar) and use it to drive plant
growth. PlantDef gains a Stages list (texture/size/growDays per stage,
inheritable via abstract parents in plants.json); a resolved PlantSet
table turns those into atlas regions and day thresholds at scene load.
New PlantGrowth component plus PlantGrowthSystem advance each plant by
in-game days from the Calendar and swap its sprite/scale at stage borders.
WorldScene scatters plants again with a seed-deterministic, varied initial
maturity, registers the calendar and growth system, and the HUD now shows
the current day. Stage durations and visuals are pure data in plants.json.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>