Soil fertility scales calendar-driven plant growth

Bump the engine submodule to f39ee9e (half-texel UV inset that removes the
black tile seams seen while zooming). Add a Fertility multiplier to
TerrainDef (forest soil rich, sand/mountain poor); plants record their
cell's fertility as PlantGrowth.GrowthRate at spawn, and the growth system
multiplies the per-frame calendar day-delta by it — so growth stays tied to
the in-game calendar and runs faster on fertile soil.

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

Mods/Core/Defs/terrain.json

@@ -4,19 +4,19 @@
     { "defName": "DeepWater", "label": "terrain.deepwater", "maxHeight": 0.30, "color": [23, 63, 95] },
     { "defName": "Water",     "label": "terrain.water",     "maxHeight": 0.42, "color": [32, 99, 155] },
     { "defName": "Sand",      "label": "terrain.sand",      "maxHeight": 0.48, "color": [237, 201, 120],
-      "isLand": true, "surface": "terrain/surfaces/sand" },
+      "isLand": true, "surface": "terrain/surfaces/sand", "fertility": 0.4 },
     { "defName": "Grass",     "label": "terrain.grass",     "maxHeight": 0.68, "color": [90, 160, 70],
-      "isLand": true, "surface": "terrain/surfaces/mossy",
+      "isLand": true, "surface": "terrain/surfaces/mossy", "fertility": 1.0,
       "scatter": [
         { "chance": 0.35, "options": ["GrassA"] },
         { "chance": 0.07, "options": ["BushA", "BushB", "BushC"] }
       ] },
     { "defName": "Forest",    "label": "terrain.forest",    "maxHeight": 0.85, "color": [44, 110, 50],
-      "isLand": true, "surface": "terrain/surfaces/soil",
+      "isLand": true, "surface": "terrain/surfaces/soil", "fertility": 1.6,
       "scatter": [
         { "chance": 0.35, "options": ["TreeOakA", "TreeOakB", "TreeBirchA", "TreeGrayPineA"] }
       ] },
     { "defName": "Mountain",  "label": "terrain.mountain",  "maxHeight": 1.01, "color": [136, 132, 128],
-      "surface": "terrain/surfaces/roughhewnrock" }
+      "surface": "terrain/surfaces/roughhewnrock", "fertility": 0.2 }
   ]
 }

src/LittleSim/Content/GameDefs.cs

@@ -33,6 +33,12 @@ public sealed class TerrainDef : Def
     /// <summary>Растительность, рассыпаемая по клеткам этого террейна.</summary>
     public List<ScatterEntry> Scatter { get; init; } = [];
 
+    /// <summary>
+    /// Плодородность почвы — множитель скорости роста растений на этом террейне (1 — норма,
+    /// больше — быстрее). Богатая лесная почва растит быстрее песка/камня.
+    /// </summary>
+    public float Fertility { get; init; } = 1f;
+
     /// <summary>Цвет тонировки из <see cref="Rgb"/>.</summary>
     public Color Tint => Rgb is [var r, var g, var b, ..] ? new(r, g, b) : Color.Magenta;
 }

src/LittleSim/Scenes/ContentHelpers.cs

@@ -56,6 +56,7 @@ internal static class ScatterSpawner
                     Species = index,
                     Stage = stage,
                     AgeDays = age,
+                    GrowthRate = terrain.Fertility,
                 }
             );
         }

src/LittleSim/Sim/PlantGrowth.cs

@@ -17,4 +17,7 @@ public struct PlantGrowth : IComponent
 
     /// <summary>Накопленный возраст в игровых днях.</summary>
     public float AgeDays;
+
+    /// <summary>Множитель скорости роста (плодородность клетки): 1 — норма, больше — быстрее.</summary>
+    public float GrowthRate;
 }

src/LittleSim/Sim/PlantGrowthSystem.cs

@@ -37,7 +37,7 @@ public sealed class PlantGrowthSystem(PlantSet plants, Calendar calendar, int ce
                     continue; // уже зрелое — рост окончен
                 }
 
-                grow.AgeDays += deltaDays;
+                grow.AgeDays += deltaDays * grow.GrowthRate; // плодородность ускоряет/замедляет рост
                 var changed = false;
                 while (
                     grow.Stage < stages.Length - 1