fix(chat): prevent sortable sidebar drags from triggering file upload overlay (#25675)

Add a custom MIME type (application/x-open-webui-drag) to intentional
chat and folder drag sources. The onDragOver handler in MessageInput
now checks for this type instead of the generic text/plain, which
SortableJS also sets during reorder operations for pinned menu items
(Notes, Workspace) and pinned Models.

src/lib/components/layout/Sidebar/RecursiveFolder.svelte

@@ -206,6 +206,10 @@
 						} catch (error) {
 							console.log('Error parsing dataTransfer:', error);
 						}
+
+						// Only process the first non-file item; all share the same
+						// text/plain payload, so continuing would duplicate the move.
+						break;
 					}
 				}
 			}
@@ -243,6 +247,7 @@
 				id: folderId
 			})
 		);
+		event.dataTransfer.setData('application/x-open-webui-drag', '');
 
 		dragged = true;
 		folderElement.style.opacity = '0.5'; // Optional: Visual cue to show it's being dragged