- MailListView: setDragEnabled, setAcceptDrops, setDropIndicatorShown, setDragDropMode(DragDrop)
- Custom MIME type: application/x-wino-mail-ids with QVector<int> mail IDs
- mousePressEvent + mouseMoveEvent for drag initiation (standard Qt drag distance)
- initDrag() creates QDrag with selected mail IDs
- dragEnterEvent, dragMoveEvent, dropEvent handlers
- dropEvent emits batchMoveRequested(mailIds, targetFolderId)
- Works in both tree view and compact list view