Try to use QSortFilterProxyModel via cxx-qt.

This may be easier if I just wrap a QAbstractItemModel in C++ and use
cxx-qt to pull it into QML? That way I could do C++ pointer things in
C++ and rust things in rust.

qml/ClideTreeView.qml

@@ -16,20 +16,23 @@ Rectangle {
 
     signal fileClicked(string filePath)
 
+    // https://doc.qt.io/qt-6/qml-qtquick-treeview.html
     TreeView {
         id: fileSystemTreeView
         anchors.margins: 15
 
         property int lastIndex: -1
 
-        model: FileSystem
+        model: FileSystemSortProxyModel {
+            id: fs
+        }
         anchors.fill: parent
         boundsBehavior: Flickable.StopAtBounds
         boundsMovement: Flickable.StopAtBounds
         clip: true
 
         Component.onCompleted: {
-            FileSystem.setDirectory(root.rootDirectory)
+            fs.setDirectory(root.rootDirectory)
             fileSystemTreeView.expandRecursively(0, -1)
         }
 
@@ -122,13 +125,13 @@ Rectangle {
                     text: qsTr("Set as root index")
                     onTriggered: {
                         console.log("Setting directory: " + treeDelegate.filePath)
-                        FileSystem.setDirectory(treeDelegate.filePath)
+                        FileSystemSortProxyModel.setDirectory(treeDelegate.filePath)
                     }
                 }
                 Action {
                     text: qsTr("Reset root index")
                     onTriggered: {
-                        FileSystem.setDirectory("")
+                        FileSystemSortProxyModel.setDirectory("")
                     }
                 }
             }