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/scene/mod.rs

@@ -1127,6 +1127,14 @@ impl Scene {
         handle
     }
 
+    /// Returns the RGBA color for the given layer name.
+    pub fn layer_color(&self, layer: &str) -> [f32; 4] {
+        let layer_entry = self.document.layers.get(layer);
+        let color = layer_entry.map(|l| &l.color).unwrap_or(&acadrust::types::Color::WHITE);
+        let [r, g, b, _] = crate::scene::tessellate::aci_to_rgba(color);
+        [r, g, b, 1.0]
+    }
+
     pub fn custom_block_names(&self) -> Vec<String> {
         self.document
             .block_records