fix: drag-to-create parent group is now an empty container

When dragging B onto A, the result is now:
- New Group (empty, no file)
  - File A
  - File B

Previously the group inherited A's file, creating a self-referencing parent.

src/views/waypoint-view.ts

@@ -1048,10 +1048,13 @@ export class WaypointView extends ItemView {
 		const newGroup: BookmarkItem = {
 			id: `bm-${Date.now()}-${Math.random().toString(36).slice(2, 6)}`,
 			type: 'group',
-			label: target.label,
+			label: 'New Group',
-			filePath: target.filePath || '',
+			filePath: '',
 			icon: '',
-			children: [{ ...target, indent: 1 }, { ...dragged, indent: 1 }],
+			children: [
+				{ ...target, indent: target.indent + 1 },
+				{ ...dragged, indent: target.indent + 1 },
+			],
 			collapsed: false,
 			indent: target.indent,
 		};