feat: BOX, SPHERE, CYLINDER primitives + EXTRUDE / REVOLVE commands

BOX, SPHERE, and CYLINDER build truck topology solids and tessellate
them into MeshModels stored alongside a Solid3D placeholder entity so
the GPU mesh pipeline renders them immediately.

EXTRUDE picks any closed 2D profile (Circle, LwPolyline, etc.),
attaches a planar face via try_attach_plane, and translational-sweeps
it (tsweep Face → Solid) along Z by the given height.

REVOLVE picks a profile, two axis points, and an angle (default 360°),
then rotational-sweeps the wire (rsweep) around the axis.

Three new CmdResult variants drive the operations:
  CommitSolid3D, ExtrudeEntity, RevolveEntity.

Scene::layer_color() added to retrieve the active layer's RGBA color.

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

src/command/mod.rs

@@ -138,6 +138,21 @@ pub enum CmdResult {
         /// Translation vector to apply to vertices inside the window.
         delta: Vec3,
     },
+    /// Create a Solid3D placeholder entity + associated MeshModel.
+    /// `mesh_fn` is called with the entity's handle string to build the mesh.
+    CommitSolid3D {
+        mesh_fn: Box<dyn FnOnce(String) -> Option<crate::scene::mesh_model::MeshModel> + Send>,
+    },
+    /// Extrude the profile entity `handle` by `height` along Z.
+    ExtrudeEntity { handle: Handle, height: f32, color: [f32; 4] },
+    /// Revolve the profile entity `handle` around the given axis by `angle_deg`.
+    RevolveEntity {
+        handle: Handle,
+        axis_start: glam::Vec3,
+        axis_end: glam::Vec3,
+        angle_deg: f32,
+        color: [f32; 4],
+    },
     /// INSERT landed on a block that has AttributeDefinitions.
     /// The host should look up the attdefs for `block_name` from the document
     /// and call `attreq_set_attdefs()` on the command, then loop on text input.