Let search results be dragged onto a folio like the tree

While a collection search is active the tree is replaced by the flat
ranked list, and that list had no drag support: dragging a result only
moved the selection. Anyone used to searching and then dragging lost the
drag as soon as they typed.

The tree's drag is moved into a static ElementsTreeView::execElementDrag()
taking the source widget, and the results list uses it from the path each
row already carries, so the drag content and pixmap are the same.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01G2d2Zi8BfrYRPX88zhaoFG

sources/ElementsCollection/elementstreeview.h

@@ -32,6 +32,8 @@ class ElementsTreeView : public QTreeView
 {
 	public:
 		ElementsTreeView(QWidget *parent = nullptr);
+		static void execElementDrag(QWidget *source,
+					    const ElementsLocation &location);
 
 	protected:
 		void startDrag(Qt::DropActions supportedActions) override;