Phase A: wire climate + day/night into the world; design doc

Bump the engine submodule to a684c23 (Climate + day/night ambient). The
world scene now registers UseClimate and UseDayNight, so it darkens at
night and the HUD shows the season and temperature alongside the date.
Add docs/растения.md capturing the whole plant-ecosystem design (growth as
a suitability product, hybrid Mendelian genome, climate, lighting with
shadows, reproduction, persistence) and the A-D phase plan.

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

src/LittleSim/Scenes/WorldScene.cs

@@ -13,6 +13,7 @@ using MrGameEng.DevConsole;
 using MrGameEng.Graphics;
 using MrGameEng.Input;
 using MrGameEng.Inspector;
+using MrGameEng.Lighting;
 using MrGameEng.Tilemaps;
 using MrGameEng.UI;
 using Myra.Graphics2D;
@@ -74,6 +75,8 @@ public sealed class WorldScene : Scene
         this.UseTilemaps();
 
         var calendar = Context.UseCalendar(SecondsPerDay);
+        var climate = Context.UseClimate(ClimateSettings.Default);
+        this.UseDayNight(renderer); // мир темнеет ночью — амбиент идёт в рендер
 
         // Рельеф и расстановка растений детерминированы сидом мира (независимые потоки seed).
         var plants = new PlantSet(content, atlases, device);
@@ -105,7 +108,15 @@ public sealed class WorldScene : Scene
             new GodCameraSystem(camera, input, renderer, console, () => _pause.IsOpen)
         );
         UpdateSystems.Add(
-            new HudSystem(Context, content.Languages, hudLabel, "hud.world", _config.Seed, calendar)
+            new HudSystem(
+                Context,
+                content.Languages,
+                hudLabel,
+                "hud.world",
+                _config.Seed,
+                calendar,
+                climate
+            )
         );
         UpdateSystems.Add(new CallbackSystem(() => Hotkeys(input)));
 

src/LittleSim/Sim/SimSystems.cs

@@ -185,7 +185,8 @@ public sealed class HudSystem(
     Myra.Graphics2D.UI.Label label,
     string titleKey,
     int seed,
-    MrGameEng.Core.Calendar? calendar = null
+    MrGameEng.Core.Calendar? calendar = null,
+    MrGameEng.Core.Climate? climate = null
 ) : BaseSystem
 {
     private float _accumulated;
@@ -206,6 +207,14 @@ public sealed class HudSystem(
         var when = calendar is null
             ? ""
             : languages.Format("hud.datetime", calendar.Day, calendar.Hour, calendar.Minute);
+        if (climate is not null)
+        {
+            var season = languages.Get("season." + climate.Season.ToString().ToLowerInvariant());
+            when +=
+                " | "
+                + languages.Format("hud.climate", season, (int)MathF.Round(climate.Temperature));
+        }
+
         label.Text =
             languages.Format(titleKey, seed, when, fps) + "\n" + languages.Get("hud.controls");
     }