Fix chat rendering and improve scroll behavior

- Emit SegmentsRole in dataChanged signals so QML updates properly
- Add onContentHeightChanged to scroll when content loads after session switch
- Add floating scroll-to-bottom button that appears when scrolled up
- Wrap chat ScrollView in Item to allow button overlay

gui/chatblockmodel.cpp

@@ -223,7 +223,7 @@ void ChatBlockModel::appendData(const QString &text)
         
         // But emit with the rendered HTML that includes partial content
         QModelIndex idx = index(m_blocks.size() - 1);
-        emit dataChanged(idx, idx, {RenderedHtmlRole});
+        emit dataChanged(idx, idx, {RenderedHtmlRole, SegmentsRole});
     }
 }
 
@@ -483,7 +483,7 @@ void ChatBlockModel::appendContent(const QString &line)
     rebuildBlockHtml(m_blocks.size() - 1);
 
     QModelIndex idx = index(m_blocks.size() - 1);
-    emit dataChanged(idx, idx, {ContentRole, RenderedHtmlRole});
+    emit dataChanged(idx, idx, {ContentRole, RenderedHtmlRole, SegmentsRole});
 }
 
 void ChatBlockModel::processLine(const QString &line)

gui/main.qml

@@ -1220,10 +1220,13 @@ ApplicationWindow {
 
             Rectangle { Layout.fillWidth: true; height: 1; color: theme.midColor }
 
-            // Chat display — block-based ListView
-            ScrollView {
+            // Chat display — block-based ListView with scroll-to-bottom button
+            Item {
                 Layout.fillWidth: true
                 Layout.fillHeight: true
+                
+                ScrollView {
+                    anchors.fill: parent
                     clip: true
 
                     // Placeholder when no agent selected or disconnected
@@ -1262,6 +1265,13 @@ ApplicationWindow {
                             }
                         }
                         
+                        onContentHeightChanged: {
+                            // Content height changed (e.g., after loading) - scroll if following
+                            if (shouldAutoScroll && count > 0) {
+                                positionViewAtEnd()
+                            }
+                        }
+
                         onCountChanged: {
                             // New block added - always scroll if we were following
                             if (count > 0) {
@@ -1587,6 +1597,38 @@ property bool blockExpanded: {
                 }
                 }
                 
+                // Scroll-to-bottom floating button
+                Rectangle {
+                    id: scrollToBottomBtn
+                    width: 40
+                    height: 40
+                    radius: 20
+                    color: theme.highlightColor
+                    opacity: 0.9
+                    anchors.right: parent.right
+                    anchors.bottom: parent.bottom
+                    anchors.margins: 16
+                    visible: !chatView.shouldAutoScroll && chatView.count > 0 && chatView.visible
+                    
+                    Label {
+                        anchors.centerIn: parent
+                        text: "↓"
+                        font.pixelSize: 20
+                        font.bold: true
+                        color: theme.highlightedTextColor
+                    }
+                    
+                    MouseArea {
+                        anchors.fill: parent
+                        cursorShape: Qt.PointingHandCursor
+                        onClicked: {
+                            chatView.shouldAutoScroll = true
+                            chatView.positionViewAtEnd()
+                        }
+                    }
+                }
+            }
+
             Rectangle { Layout.fillWidth: true; height: 1; color: theme.midColor }
 
             // Input