feat: Pinned emails support (flag/follow-up)

- EmailListModel: new m_pinnedOnly filter + setShowPinnedOnly()
- EmailListModel/EmailListModel.cpp: passes pinnedOnly to paginated queries
- MailItemDao: countAll, countByFolderId, findAllPaginated, findByFolderIdPaginated accept pinnedOnly
- MailListView: new 'Solo fijados' checkbox in filter bar
- CompactMailDelegate: orange pushpin indicator (top-right) for pinned emails
- Works in both tree view and compact card view
- Pinned indicator uses QPainterPath for pushpin shape (orange)

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

@@ -555,4 +555,6 @@ CMakeFiles/wino-mail-qt.dir/src/ui/delegates/CompactMailDelegate.cpp.o: \
  /usr/include/x86_64-linux-gnu/qt6/QtCore/QDebug \
  /usr/include/x86_64-linux-gnu/qt6/QtCore/qdebug.h \
  /usr/include/x86_64-linux-gnu/qt6/QtGui/QCursor \
- /usr/include/x86_64-linux-gnu/qt6/QtGui/qcursor.h
+ /usr/include/x86_64-linux-gnu/qt6/QtGui/qcursor.h \
+ /usr/include/x86_64-linux-gnu/qt6/QtGui/QPainterPath \
+ /usr/include/x86_64-linux-gnu/qt6/QtGui/qpainterpath.h