fix: dropdowns on a scrolled page draw their menu over the page's text

The page's widgets are laid out unscrolled and drawn scroll_y higher;
popover_offset tells the engine so, and the text under an open menu is
clipped where the menu is rather than one scroll offset below it.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

 src/main.rs | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/src/main.rs b/src/main.rs
index d84d33e..121bd0f 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -599,6 +599,17 @@ impl cce_ui::engine::Application for SystemInterface {
         Some(&mut self.ui_context)
     }
 
+    // Page widgets are laid out unscrolled and drawn `scroll_y` higher (the
+    // popover replay in `rebuild_layout` subtracts it); the chrome dropdown
+    // is in window coords already.
+    fn popover_offset(&self, id: cce_ui::widget::WidgetId) -> (f32, f32) {
+        if id == self.page_dropdown.id() {
+            (0.0, 0.0)
+        } else {
+            (0.0, -self.scroll_y)
+        }
+    }
+
     fn clear_color(&self) -> [f32; 4] {
         [0.039, 0.102, 0.055, 1.0]
     }