Split viewer and simulation into separate apps

apps/backend/Simulation/WorldService.cs

@@ -0,0 +1,36 @@
+using SpaceGame.Simulation.Api.Contracts;
+
+namespace SpaceGame.Simulation.Api.Simulation;
+
+public sealed class WorldService(IWebHostEnvironment environment)
+{
+  private readonly object _sync = new();
+  private readonly ScenarioLoader _loader = new(environment.ContentRootPath);
+  private readonly SimulationEngine _engine = new();
+  private SimulationWorld _world = new ScenarioLoader(environment.ContentRootPath).Load();
+
+  public WorldSnapshot GetSnapshot()
+  {
+    lock (_sync)
+    {
+      return _engine.BuildSnapshot(_world);
+    }
+  }
+
+  public void Tick(float deltaSeconds)
+  {
+    lock (_sync)
+    {
+      _engine.Tick(_world, deltaSeconds);
+    }
+  }
+
+  public WorldSnapshot Reset()
+  {
+    lock (_sync)
+    {
+      _world = _loader.Load();
+      return _engine.BuildSnapshot(_world);
+    }
+  }
+}