Browser multiplayer client: promote the KNI spike to src/LittleSim.Web

LittleSim.Web (Blazor WASM + KNI/WebGL) is a real network client now: it
connects to the dedicated server over WebSocket (ClientWebSocket maps to
the browser socket), applies MrGameEng.Net delta snapshots into its
EntityStore and draws pawns through SpriteBatch — fatigue dims them just
like on desktop. The server address comes from ?server=ws://host:port
in the page URL, defaulting to the page's host on port 9050. The net
contract is mirrored in NetContract.cs (KNI and DesktopGL assemblies
can't mix until the graphics libraries build per platform) with loud
keep-in-sync comments on both sides.

Both clients now smooth replicated positions between 10 Hz snapshots:
NetLerp + NetSmoothingSystem lerp the visual position toward the latest
server position every frame (exponential, ~0.25 s to converge).

Verified against a live LittleSim.Server --listen: the browser client
connects (server log), draws ~3.3k lit pixels of pawns whose layout
changes between samples, and survives 400+ ticks without errors. Found
along the way: requestAnimationFrame freezes in hidden windows — the
game loop only runs while the tab is visible.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/LittleSim.Web/LittleSimWebGame.cs

@@ -0,0 +1,62 @@
+using System;
+using Microsoft.Xna.Framework;
+using Microsoft.Xna.Framework.Graphics;
+using MrGameEng.Core;
+
+namespace LittleSim.Web;
+
+/// <summary>
+/// Веб-хост LittleSim поверх KNI (BlazorGL/WebGL) — браузерный аналог
+/// MrGameEng.Host.GameHost: владеет EngineContext ядра, гонит GameClock и фазы сцены.
+/// Цикл тикается из requestAnimationFrame (см. Pages/Index.razor.cs). Когда графика
+/// движка научится собираться под KNI, этот класс переедет в MrGameEng.Host.Web.
+/// </summary>
+public class LittleSimWebGame : Game
+{
+    /// <summary>Контекст ядра движка, общий со сценами и системами.</summary>
+    public EngineContext Context { get; } = new EngineContext();
+
+    private readonly Uri _server;
+    private GraphicsDeviceManager _graphics;
+    private SpriteBatch _spriteBatch = null!;
+    private Texture2D _pixel = null!;
+
+    /// <summary>Игра, подключающаяся к серверу <paramref name="server"/>.</summary>
+    public LittleSimWebGame(Uri server)
+    {
+        _server = server;
+        _graphics = new GraphicsDeviceManager(this);
+        Content.RootDirectory = "Content";
+    }
+
+    /// <inheritdoc />
+    protected override void Initialize()
+    {
+        base.Initialize();
+        Context.Scenes.Switch(new WorldViewScene(_server, () => _spriteBatch, () => _pixel));
+    }
+
+    /// <inheritdoc />
+    protected override void LoadContent()
+    {
+        _spriteBatch = new SpriteBatch(GraphicsDevice);
+        _pixel = new Texture2D(GraphicsDevice, 1, 1);
+        _pixel.SetData(new[] { Color.White });
+    }
+
+    /// <inheritdoc />
+    protected override void Update(GameTime gameTime)
+    {
+        Context.Clock.Advance((float)gameTime.ElapsedGameTime.TotalSeconds);
+        Context.Scenes.Update(Context.Clock);
+        base.Update(gameTime);
+    }
+
+    /// <inheritdoc />
+    protected override void Draw(GameTime gameTime)
+    {
+        GraphicsDevice.Clear(new Color(12, 16, 24));
+        Context.Scenes.Draw(Context.Clock);
+        base.Draw(gameTime);
+    }
+}