fix(node): only round a box that has a border

A filled box without one is a plain rectangle: rounding it leaves the
surface showing at the corners, which reads as a seam nobody asked for.

native/src/node/painter.h

@@ -78,13 +78,16 @@ class Painter {
     const bool hasFill = own && (own->set & S_FILL);
     if (!hasFill && !hasBorder) return;
 
-    const int32_t radius = tree.inherited(id, S_RADIUS).radius;
-    if (hasFill && radius == 0 && !hasBorder) {
+    // Only a bordered box rounds its corners. Filling a square first would leave corners
+    // outside the border, and rounding an unbordered fill puts a seam where a plain panel
+    // background was expected.
+    if (!hasBorder) {
       gui.fillRect(n.x, n.y, n.w, n.h, own->fill);
       return;
     }
     const int32_t fill = hasFill ? own->fill : tree.inherited(id, S_BG).bg;
-    gui.roundRect(n.x, n.y, n.w, n.h, radius, surfaceOf(id), &fill, &fill, hasBorder ? &own->border : nullptr);
+    gui.roundRect(n.x, n.y, n.w, n.h, tree.inherited(id, S_RADIUS).radius, surfaceOf(id), &fill, &fill,
+                  &own->border);
   }
 
   void paintButton(uint16_t id) {