Weight system: body mass, carry capacity, Kleiber metabolism

Mass is derived by a cubic law: mass = BaseMassKg * (size / reference)^3, so a
juvenile/seedling weighs far less than an adult/mature and the size gene moves
mass too. New Mass helper + BaseMassKg on AnimalDef/PlantDef (deer 70, wolf 45,
boar 80, chicken 2.5; trees ~450, grass 0.4, etc.) and MassKg per unit on
ProductDef (foundation for hauling/inventory).

Wired into the sim (as chosen):
- Corpse meat is now proportional to body mass (Mass.MeatFraction), not raw
  bodySize; Corpse gained a BodySize field so sprite scale stays independent of
  meat (save/load updated).
- Kleiber metabolism: need decay x= (mass/refMass)^0.75, normalized per species,
  so juveniles are cheaper to feed and heavier individuals eat a bit more,
  without cross-species balance blowups (adults of typical size are unchanged).
- Carry capacity = mass x fraction x carry capability (Moving for quadrupeds;
  Manipulation for future humans), shown in inspector/console. A dormant Carrier
  component + Mass.LoadSpeedFactor hook slow an overloaded animal — the
  foundation for item hauling.

Inspector shows body/plant weight (+carry); `animal`/`plant` console print mass.
Build + --check-content clean (42 genes, 41 traits). Not GUI-verified.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Mods/Core/Languages/en/ui.json

@@ -17,6 +17,8 @@
   "inspect.growing": "Growth: {0:0}% to next stage",
   "inspect.mature": "Fully grown",
   "inspect.age": "Age: {0:0.0} d · lives to {1:0}",
+  "inspect.mass": "Weight: {0:0.#} kg · carries up to {1:0.#} kg",
+  "inspect.plantmass": "Weight: {0:0.##} kg",
   "inspect.state": "State: {0}",
   "inspect.state.growing": "growing",
   "inspect.state.mature": "mature",

Mods/Core/Languages/ru/ui.json

@@ -17,6 +17,8 @@
   "inspect.growing": "Рост: {0:0}% до следующей стадии",
   "inspect.mature": "Полностью выросло",
   "inspect.age": "Возраст: {0:0.0} дн · живёт до {1:0}",
+  "inspect.mass": "Вес: {0:0.#} кг · несёт до {1:0.#} кг",
+  "inspect.plantmass": "Вес: {0:0.##} кг",
   "inspect.state": "Состояние: {0}",
   "inspect.state.growing": "растёт",
   "inspect.state.mature": "созрело",