fix(command-palette): fix Escape key not hiding command palette

This commit updates the keydown handler within the shared `Header` component to fix a bug where the main window would not hide when Escape was pressed. Previously, the component would unconditionally consume the `Escape` key press, preventing it from reaching the global handler. The logic is now conditional, only preventing the default action if a back action (`onPopView`) is defined, which restores the expected behavior for the root command palette.

src/lib/components/layout/Header.svelte

@@ -30,8 +30,10 @@
 				return;
 			}
 
-			event.preventDefault();
-			onPopView?.();
+			if (onPopView) {
+				event.preventDefault();
+				onPopView();
+			}
 		}
 	};
 </script>