fix(system): safe check all event target

packages/svelte/src/lib/container/Pane/Pane.svelte

@@ -103,7 +103,7 @@
       return;
     }
 
-    (event.target as Element)?.setPointerCapture?.(event.pointerId);
+    (event.target as Partial<Element> | null)?.setPointerCapture?.(event.pointerId);
 
     const { x, y } = getEventPosition(event, containerBounds);
 
@@ -175,7 +175,7 @@
       return;
     }
 
-    (event.target as Element)?.releasePointerCapture?.(event.pointerId);
+    (event.target as Partial<Element> | null)?.releasePointerCapture?.(event.pointerId);
 
     // We only want to trigger click functions when in selection mode if
     // the user did not move the mouse.