gui: restore scroll-follow with debounced Timer

Use a 16ms Timer restarted from onContentHeightChanged and
onCountChanged. The timer fires after the polish pass completes,
avoiding the recursive layout loop that the old synchronous
positionViewAtEnd() caused.

gui/main.qml

@@ -888,14 +888,23 @@ ApplicationWindow {
 
                     onCountChanged: {
                         if (followTail)
-                            Qt.callLater(chatView.scrollToEnd)
+                            scrollTimer.restart()
+                    }
+
+                    onContentHeightChanged: {
+                        if (followTail)
+                            scrollTimer.restart()
                     }
 
                     onMovementEnded: followTail = atYEnd
 
-                    function scrollToEnd() {
+                    Timer {
-                        if (followTail && contentHeight > height)
+                        id: scrollTimer
-                            positionViewAtEnd()
+                        interval: 16
+                        onTriggered: {
+                            if (chatView.followTail && chatView.contentHeight > chatView.height)
+                                chatView.positionViewAtEnd()
+                        }
                     }
 
                     delegate: ChatBlockDelegate {