v0.16.0 — ThemedMessageBox replacing native MessageBox everywhere

The Win32 MessageBox uses the system white-on-gray look that clashes
with the launcher's dark theme (jarring transition every time we
confirm a cancel, show an error, etc.). Replaced with a custom WPF
dialog that:

- Drops in : same Show(message, title, button, icon, default) API as
  System.Windows.MessageBox, returns the same MessageBoxResult.
- Looks native to the launcher : dark Brush.Bg.Window background,
  Brush.Border outline, Brush.Text.Primary content, AccentButton for
  the default action and SecondaryButton for the others.
- Iconography by emoji + colour code : ⛔ red (Error), ⚠ amber (Warning),
  ❓ neutral (Question), ℹ blue (Information). Mapped from MessageBoxImage.
- Buttons localised via Strings.ActionOk / ActionYes / ActionNo /
  ActionCancel — works in fr/en/zh/th/ar like the rest of the UI.
- Owner = currently active window (falls back to MainWindow then
  CenterScreen) so it positions correctly even from a child dialog.
- Esc resolves to Cancel/No matching MessageBox semantics.

The 21 MessageBox.Show call sites across MainViewModel, SettingsViewModel,
LicenseDetailsDialog and MainWindow now use ThemedMessageBox.Show with
no signature change — full grep replace + tiny `using` adjustments.

Versions bumped to 0.16.0.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/PSLauncher.App/Views/ThemedMessageBox.xaml

@@ -0,0 +1,72 @@
+<Window x:Class="PSLauncher.App.Views.ThemedMessageBox"
+        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:loc="clr-namespace:PSLauncher.Core.Localization;assembly=PSLauncher.Core"
+        Title=""
+        Icon="pack://application:,,,/Resources/favicon.ico"
+        SizeToContent="Height"
+        Width="480"
+        MinHeight="180"
+        MaxHeight="600"
+        ResizeMode="NoResize"
+        ShowInTaskbar="False"
+        WindowStartupLocation="CenterOwner"
+        Background="{StaticResource Brush.Bg.Window}">
+    <Border BorderBrush="{StaticResource Brush.Border}" BorderThickness="1">
+        <Grid Margin="24,20">
+            <Grid.RowDefinitions>
+                <RowDefinition Height="Auto" />
+                <RowDefinition Height="*" />
+                <RowDefinition Height="Auto" />
+            </Grid.RowDefinitions>
+
+            <!-- Title -->
+            <TextBlock Grid.Row="0"
+                       x:Name="TitleText"
+                       FontSize="16" FontWeight="SemiBold"
+                       Foreground="{StaticResource Brush.Text.Primary}"
+                       Margin="0,0,0,12" />
+
+            <!-- Icon + Message -->
+            <Grid Grid.Row="1">
+                <Grid.ColumnDefinitions>
+                    <ColumnDefinition Width="Auto" />
+                    <ColumnDefinition Width="*" />
+                </Grid.ColumnDefinitions>
+                <TextBlock Grid.Column="0"
+                           x:Name="IconText"
+                           FontSize="36"
+                           Margin="0,2,16,0"
+                           VerticalAlignment="Top" />
+                <TextBlock Grid.Column="1"
+                           x:Name="MessageText"
+                           TextWrapping="Wrap"
+                           FontSize="13" LineHeight="20"
+                           Foreground="{StaticResource Brush.Text.Primary}"
+                           VerticalAlignment="Center" />
+            </Grid>
+
+            <!-- Buttons -->
+            <StackPanel Grid.Row="2"
+                        Orientation="Horizontal"
+                        HorizontalAlignment="Right"
+                        Margin="0,24,0,0">
+                <Button x:Name="Btn1"
+                        Style="{StaticResource SecondaryButton}"
+                        MinWidth="80" Padding="16,8" Margin="0,0,8,0"
+                        Visibility="Collapsed"
+                        Click="OnBtn1Click" />
+                <Button x:Name="Btn2"
+                        Style="{StaticResource SecondaryButton}"
+                        MinWidth="80" Padding="16,8" Margin="0,0,8,0"
+                        Visibility="Collapsed"
+                        Click="OnBtn2Click" />
+                <Button x:Name="Btn3"
+                        Style="{StaticResource AccentButton}"
+                        MinWidth="80" Padding="16,8"
+                        Visibility="Collapsed"
+                        Click="OnBtn3Click" />
+            </StackPanel>
+        </Grid>
+    </Border>
+</Window>