feat: spawn spheres via MCP — shape parameter cube/sphere

- SpawnModelCommand: added Shape property (default 'cube')
- AiCommandProcessor: if shape='sphere', uses ProceduralMesh.CreateSphere
  instead of loading OBJ file; physics uses DynamicSphere instead of DynamicBox
- EngineMcpTools: added 'shape' parameter to SpawnModel tool
- Engine.AI now references Engine.Graphics for ProceduralMesh access

src/Engine.AI/AiCommandProcessor.cs

@@ -6,6 +6,7 @@ using Engine.AI.Commands;
 using Engine.AI.Serialization;
 using Engine.Core;
 using Engine.Core.Components;
+using Engine.Graphics;
 using Flecs.NET.Core;
 
 namespace Engine.AI;
@@ -78,7 +79,17 @@ public sealed class AiCommandProcessor
 
     private AiCommandResult SpawnModel(SpawnModelCommand command)
     {
-        var mesh = _modelLoader(command.ModelPath);
+        Mesh mesh;
+        if (command.Shape == "sphere")
+        {
+            var r = MathF.Max(MathF.Max(command.Scale.X, command.Scale.Y), command.Scale.Z) * 0.5f;
+            mesh = ProceduralMesh.CreateSphere(r, 24, 12, new Vector3(0.5f, 0.6f, 0.9f));
+        }
+        else
+        {
+            mesh = _modelLoader(command.ModelPath);
+        }
+
         var entity = _world.Entity(command.Name)
             .Set(new Transform(command.Position, command.Rotation, command.Scale))
             .Set(mesh);
@@ -86,11 +97,17 @@ public sealed class AiCommandProcessor
         if (command.Physics)
         {
             var maxScale = MathF.Max(MathF.Max(command.Scale.X, command.Scale.Y), command.Scale.Z);
-            var rb = RigidBody.DynamicBox(new Vector3(maxScale * 0.5f), mass: maxScale * 2f);
-            entity.Set(rb);
+            if (command.Shape == "sphere")
+            {
+                entity.Set(RigidBody.DynamicSphere(maxScale * 0.5f, mass: maxScale * 2f));
+            }
+            else
+            {
+                entity.Set(RigidBody.DynamicBox(new Vector3(maxScale * 0.5f), mass: maxScale * 2f));
+            }
         }
 
-        return AiCommandResult.Ok($"Spawned entity '{command.Name}' with model '{command.ModelPath}' (id {(ulong)entity.Id}).");
+        return AiCommandResult.Ok($"Spawned entity '{command.Name}' with shape '{command.Shape}' (id {(ulong)entity.Id}).");
     }
 
     private AiCommandResult SetTransform(SetTransformCommand command)

src/Engine.AI/Commands/SpawnModelCommand.cs

@@ -13,4 +13,5 @@ public sealed record SpawnModelCommand : AiCommand
     public Quaternion Rotation { get; init; } = Quaternion.Identity;
     public Vector3 Scale { get; init; } = Vector3.One;
     public bool Physics { get; init; } = false;
+    public string Shape { get; init; } = "cube";
 }

src/Engine.AI/Engine.AI.csproj

@@ -13,6 +13,7 @@
 
   <ItemGroup>
     <ProjectReference Include="..\Engine.Core\Engine.Core.csproj" />
+    <ProjectReference Include="..\Engine.Graphics\Engine.Graphics.csproj" />
   </ItemGroup>
 
   <ItemGroup Condition="'$(Configuration)' != 'ReleaseAOT'">

src/Engine.AI/Mcp/EngineMcpTools.cs

@@ -25,7 +25,8 @@ public sealed class EngineMcpTools
         [Description("Optional position as [x, y, z] (default: 0,0,0)")] IReadOnlyList<double>? position = null,
         [Description("Optional rotation as [x, y, z, w] quaternion (default: identity)")] IReadOnlyList<double>? rotation = null,
         [Description("Optional scale as [x, y, z] (default: 1,1,1)")] IReadOnlyList<double>? scale = null,
-        [Description("Optional: enable physics (default: false)")] bool physics = false)
+        [Description("Optional: enable physics (default: false)")] bool physics = false,
+        [Description("Optional: shape type 'cube' or 'sphere' (default: cube)")] string shape = "cube")
     {
         var cmd = new SpawnModelCommand
         {
@@ -34,7 +35,8 @@ public sealed class EngineMcpTools
             Position = ToVector3(position, Vector3.Zero),
             Rotation = ToQuaternion(rotation, Quaternion.Identity),
             Scale = ToVector3(scale, Vector3.One),
-            Physics = physics
+            Physics = physics,
+            Shape = shape
         };
 
         return EnqueueAndReturnMessage(cmd);