feat: Drag & drop between folders

- 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

build/CMakeFiles/wino-mail-qt.dir/compiler_depend.internal

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  /usr/include/x86_64-linux-gnu/qt6/QtGui/QColor
+ /usr/include/x86_64-linux-gnu/qt6/QtGui/QDrag
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+ /usr/include/x86_64-linux-gnu/qt6/QtGui/qdrag.h
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build/CMakeFiles/wino-mail-qt.dir/compiler_depend.make

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+  /usr/include/x86_64-linux-gnu/qt6/QtCore/qmimedata.h \
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@@ -42735,6 +42739,10 @@ wino-mail-qt_autogen/GQ6NBGVJMG/moc_accountservice.cpp:
 
 /usr/include/x86_64-linux-gnu/qt6/QtWidgets/QScrollBar:
 
+/usr/include/x86_64-linux-gnu/qt6/QtGui/qdrag.h:
+
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+
 /usr/include/x86_64-linux-gnu/qt6/QtGui/qpainterpath.h:
 
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@@ -43959,6 +43967,8 @@ CMakeFiles/wino-mail-qt.dir/src/services/synchronizer.cpp.o:
 
 /mnt/c/Users/javie/Documents/Codex/2026-08-11/revisar-2/wino-mail-dtkqt/icons.qrc:
 
+/usr/include/x86_64-linux-gnu/qt6/QtCore/QMimeData:
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 /usr/include/x86_64-linux-gnu/qt6/QtCore/qlist.h:

build/CMakeFiles/wino-mail-qt.dir/src/ui/maillistview.cpp.o.d

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- /usr/include/x86_64-linux-gnu/qt6/QtWidgets/qmenu.h
+ /usr/include/x86_64-linux-gnu/qt6/QtWidgets/qmenu.h \
+ /usr/include/x86_64-linux-gnu/qt6/QtGui/QDrag \
+ /usr/include/x86_64-linux-gnu/qt6/QtGui/qdrag.h \
+ /usr/include/x86_64-linux-gnu/qt6/QtCore/QMimeData \
+ /usr/include/x86_64-linux-gnu/qt6/QtCore/qmimedata.h