v1.08 — Custom Fluent confirmation dialog, replace all MessageBox

- New ConfirmDialog overlay with dark backdrop, rounded card, shadow
- Warning/Question/Error icon types with accent colors
- Replaced all MessageBox.Show calls (RemovePage, PreInstallCheck, Troubleshoot)
- Click outside dialog = cancel

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

Pages/ConfirmDialog.xaml

@@ -0,0 +1,41 @@
+<UserControl x:Class="InstaSoftOfficeTool.Pages.ConfirmDialog"
+             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             Visibility="Collapsed">
+
+    <!-- Backdrop overlay -->
+    <Grid>
+        <Border Background="#66000000" MouseDown="Backdrop_MouseDown"/>
+
+        <!-- Dialog card -->
+        <Border Background="{StaticResource CardBrush}" CornerRadius="12"
+                HorizontalAlignment="Center" VerticalAlignment="Center"
+                MinWidth="400" MaxWidth="500" Padding="28,24">
+            <Border.Effect>
+                <DropShadowEffect ShadowDepth="8" BlurRadius="32" Opacity="0.2" Color="Black"/>
+            </Border.Effect>
+
+            <StackPanel>
+                <!-- Icon + Title -->
+                <StackPanel Orientation="Horizontal" Margin="0,0,0,12">
+                    <TextBlock x:Name="DialogIcon" FontFamily="Segoe MDL2 Assets" FontSize="22"
+                               VerticalAlignment="Center" Margin="0,0,12,0"/>
+                    <TextBlock x:Name="DialogTitle" FontSize="18" FontWeight="SemiBold"
+                               VerticalAlignment="Center"/>
+                </StackPanel>
+
+                <!-- Message -->
+                <TextBlock x:Name="DialogMessage" FontSize="14" TextWrapping="Wrap"
+                           Foreground="{StaticResource TextSecondaryBrush}" Margin="0,0,0,24"/>
+
+                <!-- Buttons -->
+                <StackPanel Orientation="Horizontal" HorizontalAlignment="Right">
+                    <Button x:Name="BtnCancel" Style="{StaticResource SecondaryButton}"
+                            Click="BtnCancel_Click" Margin="0,0,8,0"/>
+                    <Button x:Name="BtnConfirm" Style="{StaticResource PrimaryButton}"
+                            Click="BtnConfirm_Click"/>
+                </StackPanel>
+            </StackPanel>
+        </Border>
+    </Grid>
+</UserControl>