Refactor backend into domain-first slices

apps/backend/Universe/Simulation/SimulationHostedService.cs

@@ -0,0 +1,19 @@
+namespace SpaceGame.Api.Universe.Simulation;
+
+public sealed class SimulationHostedService(WorldService worldService) : BackgroundService
+{
+  protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+  {
+    using var timer = new PeriodicTimer(TimeSpan.FromMilliseconds(200));
+    try
+    {
+      while (!stoppingToken.IsCancellationRequested && await timer.WaitForNextTickAsync(stoppingToken))
+      {
+        worldService.Tick(0.2f);
+      }
+    }
+    catch (OperationCanceledException) when (stoppingToken.IsCancellationRequested)
+    {
+    }
+  }
+}