Sync the folder after saving, and save from the command line through a temporary file

QSaveFile writes a new file, forces it to disk and renames it over the
old one, but does not force the folder to disk. On ext4 or XFS a power
cut soon after a save can then lose the rename: the previous file comes
back, or none. QET::syncFolderOf() now syncs the folder after every
project, symbol and title block save (QET::writeXmlText()) and every
.qetz save (QetZip::write()). Nothing to do on Windows.

--resave and --set-titleblock wrote a .qet straight over the output file
(QFile, truncate, write): a run stopped part-way left half a project.
They now write through QET::writeXmlText() like the GUI's save. On
Windows their .qet now has LF line ends, as the GUI writes.

Checked with strace on --resave: fdatasync of the new file, linkat into
place, fsync of the folder. The .qet written is byte-identical to before.
ctest 106/106.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

sources/qet.cpp

@@ -19,6 +19,7 @@
 #include "qetapp.h"
 #include "qeticons.h"
 #include "shortcutmanager.h"
+#include "utils/syncfolder.h"
 
 #include <cmath>
 #include <limits>
@@ -809,6 +810,7 @@ bool QET::writeXmlText(const QString &text, const QString &filepath, QString *er
 
 		return false;
 	}
+	syncFolderOf(filepath);
 
 	return(true);
 }