Refactor backend into domain-first slices

apps/backend/Universe/Api/GetWorldHealthHandler.cs

@@ -0,0 +1,23 @@
+using FastEndpoints;
+
+namespace SpaceGame.Api.Universe.Api;
+
+public sealed class GetWorldHealthHandler(WorldService worldService) : EndpointWithoutRequest
+{
+  public override void Configure()
+  {
+    Get("/api/world/health");
+    AllowAnonymous();
+  }
+
+  public override Task HandleAsync(CancellationToken cancellationToken)
+  {
+    var status = worldService.GetStatus();
+    return SendOkAsync(new
+    {
+      ok = true,
+      sequence = status.Sequence,
+      generatedAtUtc = status.GeneratedAtUtc,
+    }, cancellationToken);
+  }
+}