fix: guard against unwrap panic in layout and more try_borrow fixes

- layout_stack: replace unwrap() on get_widget_info with graceful fallback
- handle_scroll: use try_borrow for widget kind lookup

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Ralph Kuepper

crates/perry-ui-windows/src/layout.rs

@@ -100,7 +100,10 @@ fn layout_stack(handle: i64, width: i32, height: i32, vertical: bool) {
     let mut child_sizes: Vec<i32> = Vec::new();
 
     for &child in &visible_children {
-        let ci = widgets::get_widget_info(child).unwrap();
+        let ci = match widgets::get_widget_info(child) {
+            Some(ci) => ci,
+            None => { child_sizes.push(0); continue; }
+        };
         if matches!(ci.kind, WidgetKind::Spacer) || ci.fills_remaining {
             child_sizes.push(0); // placeholder, will be computed below
         } else if !vertical && ci.fixed_width.is_some() {