chore: root-surface radius from window_silhouette_radius (cce-ui RFC 7b-2)

The root-surface corner radius now reads the silhouette scalar (shared
nominal x corner-span factor) instead of the un-spanned per-app value, so
the drawn arc matches the compositor's clip. Verified: diffs confined to
the corner arcs.

 src/main.rs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/main.rs b/src/main.rs
index e5be7aa..fc719f0 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -634,7 +634,8 @@ impl ColorApp {
                 if c[3] > 0.001 {
                     c[3] = cce_ui::color::root_plate_opacity();
                 }
-                let radius = cce_ui::colors::root_plate_corner_radius();
+                // Silhouette radius (cce-ui RFC 7b).
+                let radius = cce_ui::layout::window_silhouette_radius();
                 (c, 0.0, 0.0, self.width as f32, self.height as f32, radius.max(0.0), (radius > 0.1, radius > 0.1, radius > 0.1, radius > 0.1))
             };
             if self.window_focused {