feat(backend): move endpoints to FastEndpoints handlers

apps/backend/Handlers/GetWorldHandler.cs

@@ -0,0 +1,16 @@
+using FastEndpoints;
+using SpaceGame.Simulation.Api.Simulation;
+
+namespace SpaceGame.Simulation.Api.Handlers;
+
+public sealed class GetWorldHandler(WorldService worldService) : EndpointWithoutRequest
+{
+  public override void Configure()
+  {
+    Get("/api/world");
+    AllowAnonymous();
+  }
+
+  public override Task HandleAsync(CancellationToken cancellationToken) =>
+    SendOkAsync(worldService.GetSnapshot(), cancellationToken);
+}