Motori multipli: Codex e interruttore CLI nelle Impostazioni

Introduce l'astrazione Engine (Claude Code, Codex) con argomenti e parser
propri e EngineRunner come unico punto di avvio, al posto di Claude.cs. Il
JSON delle chat salva motore e id di sessione (i file vecchi restano chat di
Claude Code). Cambiare CLI apre una nuova chat; modelli ed effort seguono il
motore; un motore non installato non è selezionabile. La CLI accetta
--engine <id>. Codex gira in sola lettura e la sessione si legge da
thread.started.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

Gui/MainWindow.axaml

@@ -93,7 +93,7 @@
                     <SelectableTextBlock Text="{Binding Text}" TextWrapping="Wrap" />
                   </Border>
                   <StackPanel IsVisible="{Binding IsAi}" Spacing="6">
-                    <TextBlock Text="Claude" FontWeight="SemiBold" FontSize="13.5" Foreground="{DynamicResource Accent}" />
+                    <TextBlock Text="{Binding Author}" FontWeight="SemiBold" FontSize="13.5" Foreground="{DynamicResource Accent}" />
                     <gui:MarkdownView Source="{Binding Text}" />
                     <Button Classes="ghost" HorizontalAlignment="Left" MinHeight="30" Padding="10,0" FontSize="13" Content="Copia"
                             Command="{Binding $parent[ItemsControl].((gui:MainViewModel)DataContext).CopyCommand}" CommandParameter="{Binding Text}"
@@ -108,7 +108,7 @@
           <!-- Attesa -->
           <StackPanel IsVisible="{Binding IsBusy}" Orientation="Horizontal" Spacing="12">
             <ProgressBar IsIndeterminate="True" Width="80" Height="4" Foreground="{DynamicResource Accent}" VerticalAlignment="Center" />
-            <TextBlock Text="Claude sta scrivendo…" Foreground="{DynamicResource FgMuted}" />
+            <TextBlock Text="{Binding BusyText}" Foreground="{DynamicResource FgMuted}" />
           </StackPanel>
         </StackPanel>
       </ScrollViewer>
@@ -125,7 +125,19 @@
           <Flyout Placement="BottomEdgeAlignedRight">
             <StackPanel Width="300" Spacing="6" Margin="4">
               <TextBlock Text="Impostazioni" FontWeight="SemiBold" Margin="0,0,0,6" />
-              <TextBlock Text="Modello" FontSize="13" Foreground="{DynamicResource FgMuted}" />
+              <TextBlock Text="CLI" FontSize="13" Foreground="{DynamicResource FgMuted}" />
+              <ComboBox ItemsSource="{Binding EngineChoices}" SelectedItem="{Binding SelectedEngine}" IsEnabled="{Binding CanSwitchEngine}"
+                        HorizontalAlignment="Stretch" AutomationProperties.Name="CLI (motore)">
+                <ComboBox.Styles>
+                  <Style Selector="ComboBoxItem" x:DataType="gui:EngineChoice">
+                    <Setter Property="IsEnabled" Value="{Binding Installed}" />
+                  </Style>
+                </ComboBox.Styles>
+                <ComboBox.ItemTemplate>
+                  <DataTemplate x:DataType="gui:EngineChoice"><TextBlock Text="{Binding Label}" /></DataTemplate>
+                </ComboBox.ItemTemplate>
+              </ComboBox>
+              <TextBlock Text="Modello" FontSize="13" Foreground="{DynamicResource FgMuted}" Margin="0,8,0,0" />
               <ComboBox ItemsSource="{Binding ModelChoices}" SelectedItem="{Binding SelectedModel}" HorizontalAlignment="Stretch"
                         AutomationProperties.Name="Modello">
                 <ComboBox.ItemTemplate>
@@ -151,7 +163,7 @@
         <Border Classes="composer" Background="{DynamicResource Surface}" BorderBrush="{DynamicResource Border}" BorderThickness="1" CornerRadius="20" Padding="14,10">
           <Grid ColumnDefinitions="*,Auto">
             <TextBox x:Name="InputBox" Classes="bare" Text="{Binding Input, Mode=TwoWay}" AcceptsReturn="True" TextWrapping="Wrap" MaxHeight="200"
-                     PlaceholderText="Scrivi un messaggio a Claude…" BorderThickness="0" Background="Transparent"
+                     PlaceholderText="{Binding InputPlaceholder}" BorderThickness="0" Background="Transparent"
                      VerticalContentAlignment="Center" AutomationProperties.Name="Messaggio" />
             <Button Grid.Column="1" Classes="send" VerticalAlignment="Bottom" Margin="8,0,0,0" Command="{Binding SendCommand}" AutomationProperties.Name="Invia messaggio">
               <Viewbox Width="18" Height="18"><Path Data="M12 19V5M5 12L12 5L19 12" Stroke="{Binding $parent[Button].Foreground}" StrokeThickness="2.2" StrokeLineCap="Round" StrokeJoin="Round" /></Viewbox>