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/scene/view/render.rs

@@ -2802,7 +2802,7 @@ fn viewport_override(
         .find_map(|(handle, value)| (handle == viewport).then_some(value))
 }
 
-pub(in crate::scene) fn render_style_for_viewport(
+pub(crate) fn render_style_for_viewport(
     document: &CadDocument,
     e: &EntityType,
     viewport: Option<Handle>,