feat(battle-node): WebSocket endpoint at /socket.io/ + DI extension methods

SVSim.BattleNode/Hosting/BattleNodeExtensions.cs

@@ -0,0 +1,32 @@
+// SVSim.BattleNode/Hosting/BattleNodeExtensions.cs
+using Microsoft.AspNetCore.Builder;
+using Microsoft.Extensions.DependencyInjection;
+using SVSim.BattleNode.Bridge;
+using SVSim.BattleNode.Sessions;
+
+namespace SVSim.BattleNode.Hosting;
+
+public static class BattleNodeExtensions
+{
+    public static IServiceCollection AddBattleNode(this IServiceCollection services, Action<BattleNodeOptions>? configure = null)
+    {
+        var options = new BattleNodeOptions();
+        configure?.Invoke(options);
+        services.AddSingleton(options);
+        services.AddSingleton<IBattleSessionStore, InMemoryBattleSessionStore>();
+        services.AddSingleton<IMatchingBridge, MatchingBridge>();
+        services.AddSingleton<BattleNodeWebSocketHandler>();
+        return services;
+    }
+
+    public static IApplicationBuilder UseBattleNode(this IApplicationBuilder app)
+    {
+        app.UseWebSockets();
+        app.Map("/socket.io", branch => branch.Run(async ctx =>
+        {
+            var handler = ctx.RequestServices.GetRequiredService<BattleNodeWebSocketHandler>();
+            await handler.HandleAsync(ctx);
+        }));
+        return app;
+    }
+}