[gui:] added pdf export button (unfunctional)

MainWindow.axaml

@@ -218,9 +218,18 @@
                     </TabItem.Header>
                     <Grid ColumnDefinitions="*,*">
                         <ListBox x:Name="LbResult" Margin="10,10,10,10"></ListBox>
-                        <ScrollViewer Grid.Column="1">
+                        <StackPanel Orientation="Vertical" Grid.Column="1" Spacing="10">
+                            <Button Margin="0,10,0,0" x:Name="BtnExportCoursePDF" VerticalAlignment="Top" Height="35" HorizontalAlignment="Stretch" Click="BtnExportCoursePDF_OnClick" HorizontalContentAlignment="Center">
+                                <StackPanel Orientation="Horizontal">
+                                    <LucideIcon Kind="FileText" Width="24" Height="24" />
+                                    <Label Content="Export (PDF)..." VerticalContentAlignment="Center" FontSize="12"
+                                           FontWeight="Bold" />
+                                </StackPanel>
+                            </Button>
+                            <ScrollViewer>
                                 <TextBlock x:Name="TbResultStatistics"></TextBlock>
                             </ScrollViewer>
+                        </StackPanel>
                     </Grid>
                 </TabItem>
             </TabControl>

MainWindow.axaml.cs

@@ -377,4 +377,9 @@ public partial class MainWindow : Window
             RefreshCoursesList();
         } catch (Exception ex){}
     }
+
+    private void BtnExportCoursePDF_OnClick(object? sender, RoutedEventArgs e)
+    {
+        // Export as PDF
+    }
 }