Refactor world bootstrap and allow empty startup worlds

apps/backend/Universe/Scenario/WorldTopologyBuilder.cs

@@ -0,0 +1,29 @@
+using SpaceGame.Api.Universe.Bootstrap;
+
+namespace SpaceGame.Api.Universe.Scenario;
+
+public sealed class WorldTopologyBuilder(
+    IStaticDataProvider staticData,
+    SystemGenerationService generationService,
+    SpatialBuilder spatialBuilder)
+{
+    public WorldBuildTopology Build(WorldGenerationOptions worldGenerationOptions)
+    {
+        var systems = generationService.GenerateSystems(
+          generationService.PrepareKnownSystems(staticData.KnownSystems),
+          worldGenerationOptions);
+
+        var systemRuntimes = systems
+          .Select(definition => new SystemRuntime
+          {
+              Definition = definition,
+              Position = LoaderSupport.ToVector(definition.Position),
+          })
+          .ToList();
+
+        var systemsById = systemRuntimes.ToDictionary(system => system.Definition.Id, StringComparer.Ordinal);
+        var spatialLayout = spatialBuilder.BuildLayout(systemRuntimes);
+
+        return new WorldBuildTopology(systems, systemRuntimes, systemsById, spatialLayout);
+    }
+}