Actually position the view at the end

It turns out that for whatever reason ListView.posiitionViewAtEnd() ignores any whitespace. This means that when we use the function it goes to the last delegate. This is no good as we have some padding at the bottom to make space for the typing indicator.

So the fix for this is stupid and involves adding a "spacer" delegate to the timeline beginning model which is completely invisible but qml see as a delegate so we can both leave the space and properly position the view at the end.

BUG: 501075

src/timeline/SpacerDelegate.qml

@@ -0,0 +1,11 @@
+// SPDX-FileCopyrightText: 2025 James Graham <james.h.graham@protonmail.com>
+// SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
+
+import QtQuick
+
+import org.kde.kirigami as Kirigami
+
+Item {
+    width: parent?.width
+    height: Kirigami.Units.largeSpacing + Math.round(Kirigami.Theme.defaultFont.pointSize * 2)
+}