refactor: corner reads via Element::corner_style (cce-ui 6bd batch 2)

corner_radius/rounded_corners left the Element trait; the aggregate loops
read both through the single corner_style() pair now. Behavior-preserving.

Co-Authored-By: Claude Fable 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_018u7qTwzX95dd5ysAkaSCLk

 src/json_layout.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/json_layout.rs b/src/json_layout.rs
index 70c2ad0..b20a77c 100644
--- a/src/json_layout.rs
+++ b/src/json_layout.rs
@@ -364,7 +364,7 @@ impl JsonLayoutWidget {
                 continue;
             }
             let (wx, wy, ww, wh) = w.widget.as_dyn().rect();
-            let has_rounded = w.widget.as_dyn().rounded_corners() != (false, false, false, false);
+            let has_rounded = w.widget.as_dyn().corner_style().1 != (false, false, false, false);
             if !has_rounded {
                 push_clipped(wx, wy, ww, wh, w.widget.as_dyn().color(), &mut quads);
             }