feat(ui): show color swatch and layer in selection cycling popup

Improve the selection-cycling list box so overlapping objects can be
identified at a glance:

- Add a color swatch per row showing the object's effective drawn color
- Show the layer name right-aligned next to the element type
- Size the popup to fit its content with consistent padding

Widen render_style_for_viewport visibility from scene-internal to
crate-wide so the view layer resolves the same color the renderer uses.

src/app/view/mod.rs

@@ -1435,13 +1435,23 @@ impl OpenCADStudio {
         // Selection-cycling list box: pick among overlapping objects.
         if let Some((pt, cands)) = &self.cycle_candidates {
             if !tab.is_start {
-                let items: Vec<(acadrust::Handle, String)> = cands
+                let items: Vec<crate::ui::popup::cycle_popup::CycleCandidate> = cands
                     .iter()
                     .filter_map(|&h| {
-                        tab.scene
-                            .document
-                            .get_entity(h)
-                            .map(|e| (h, crate::entities::traits::entity_type_name(e).to_string()))
+                        tab.scene.document.get_entity(h).map(|e| {
+                            let style = crate::scene::view::render::render_style_for_viewport(
+                                &tab.scene.document,
+                                e,
+                                None,
+                            );
+                            crate::ui::popup::cycle_popup::CycleCandidate {
+                                handle: h,
+                                type_name: crate::entities::traits::entity_type_name(e)
+                                    .to_string(),
+                                layer: e.common().layer.clone(),
+                                color: style.0,
+                            }
+                        })
                     })
                     .collect();
                 if !items.is_empty() {