Bring plants back as data-driven growth stages over the calendar

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>

Mods/Core/Languages/en/ui.json

@@ -1,5 +1,5 @@
 {
-  "hud.world": "LittleSim | seed {0} | {2} FPS",
+  "hud.world": "LittleSim | seed {0} | day {1} | {2} FPS",
   "hud.controls": "WASD — camera, wheel — zoom, ` — console ('help' lists commands)",
   "hud.paused": "PAUSED",
 
@@ -67,6 +67,10 @@
   "plant.pine": "pine",
   "plant.grass": "grass tuft",
   "plant.bush": "bush",
+  "plant.stage.seedling": "seedling",
+  "plant.stage.sprout": "sprout",
+  "plant.stage.sapling": "sapling",
+  "plant.stage.mature": "mature",
 
   "pawn.being": "being",
   "pawn.bear": "bear",

Mods/Core/Languages/ru/ui.json

@@ -1,5 +1,5 @@
 {
-  "hud.world": "LittleSim | сид {0} | {2} FPS",
+  "hud.world": "LittleSim | сид {0} | день {1} | {2} FPS",
   "hud.controls": "WASD — камера, колесо — зум, ` — консоль ('help' — список команд)",
   "hud.paused": "ПАУЗА",
 
@@ -67,6 +67,10 @@
   "plant.pine": "сосна",
   "plant.grass": "пучок травы",
   "plant.bush": "куст",
+  "plant.stage.seedling": "росток",
+  "plant.stage.sprout": "всходы",
+  "plant.stage.sapling": "саженец",
+  "plant.stage.mature": "взрослое",
 
   "pawn.being": "житель",
   "pawn.bear": "медведь",