Add MrGameEng.Tilemaps: code-built tile grids rendered through the batcher

TileSet maps ids to texture regions with tints (0 = empty), TileGrid is a
bounds-checked dense ushort grid, and the Tilemap component places a grid
in the world per render layer. UseTilemaps() inserts TilemapRenderSystem
before the flush; it submits only the camera-visible cell range
(TilemapMath.VisibleCells), so frame cost scales with the screen, not the
grid. Demonstrated in the sample as a checkerboard floor; Tiled loading
stays on the roadmap on top of this API.

samples/MrGameEng.Sample/Scenes/MainScene.cs

@@ -7,6 +7,7 @@ using MrGameEng.Core;
 using MrGameEng.DevConsole;
 using MrGameEng.Graphics;
 using MrGameEng.Input;
+using MrGameEng.Tilemaps;
 using MrGameEng.UI;
 using Myra.Graphics2D.UI;
 
@@ -32,6 +33,7 @@ public sealed class MainScene : Scene
 
         var renderer = this.UseRenderer2D(new Renderer2DOptions { VirtualResolution = new Point(1280, 720) });
         SampleLayers.EnsureRegistered(renderer);
+        this.UseTilemaps();
 
         var playerTexture = assets.Load(GameAssets.Textures.Player);
         var shapesTexture = assets.Load(GameAssets.Textures.Shapes);
@@ -50,6 +52,26 @@ public sealed class MainScene : Scene
             new Texture2DRegion(shapesTexture, new Rectangle(32, 32, 32, 32)),
         };
 
+        // Тайловая площадка под стартовой зоной: шахматный пол, строится кодом из TileSet/TileGrid.
+        // Видимые клетки сабмитятся каждый кадр; Depth -10 кладёт пол под декорации.
+        var floorTiles = new TileSet();
+        var floorA = floorTiles.Add(shapeRegions[0], new Color(70, 75, 95));
+        var floorB = floorTiles.Add(shapeRegions[2], new Color(55, 60, 78));
+        var floorGrid = new TileGrid(24, 14);
+        for (var y = 0; y < floorGrid.Height; y++)
+        {
+            for (var x = 0; x < floorGrid.Width; x++)
+            {
+                floorGrid[x, y] = (x + y) % 2 == 0 ? floorA : floorB;
+            }
+        }
+
+        Store.CreateEntity(new Tilemap(floorGrid, floorTiles, tileSize: 48f)
+        {
+            Origin = new Vector2(-24 * 24f, -14 * 24f),
+            Depth = -10f,
+        });
+
         // Декорации по всему миру: уезжаешь камерой — попадают под culling (см. заголовок окна).
         var random = new Random(42);
         for (var i = 0; i < DecorCount; i++)