v1.06 — Fix product key paste across all 5 fields

- Use DataObject.Pasting handler to intercept paste before MaxLength truncation
- Full key paste (e.g. XXXXX-XXXXX-XXXXX-XXXXX-XXXXX) distributes across all boxes
- Works when pasting into any of the 5 fields

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

MainWindow.xaml

@@ -42,7 +42,7 @@
                                    Foreground="{StaticResource TextSecondaryBrush}" Margin="0,-2,0,0"/>
                     </StackPanel>
                 </StackPanel>
-                <TextBlock Text="v1.05" HorizontalAlignment="Right" VerticalAlignment="Center"
+                <TextBlock Text="v1.06" HorizontalAlignment="Right" VerticalAlignment="Center"
                            FontSize="12" Foreground="{StaticResource TextSecondaryBrush}"/>
             </Grid>
         </Border>