feat(ui): add MainWindow XAML with participants DataGrid, settings sidebar, alert banner

src/TeamsISO.App/Converters/BoolToVisibilityConverter.cs

@@ -0,0 +1,18 @@
+using System.Globalization;
+using System.Windows;
+using System.Windows.Data;
+
+namespace TeamsISO.App.Converters;
+
+[ValueConversion(typeof(bool), typeof(Visibility))]
+public sealed class BoolToVisibilityConverter : IValueConverter
+{
+    public Visibility TrueValue { get; set; } = Visibility.Visible;
+    public Visibility FalseValue { get; set; } = Visibility.Collapsed;
+
+    public object Convert(object value, Type targetType, object parameter, CultureInfo culture) =>
+        value is true ? TrueValue : FalseValue;
+
+    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) =>
+        throw new NotSupportedException();
+}

src/TeamsISO.App/Converters/EnumDescriptionConverter.cs

@@ -0,0 +1,52 @@
+using System.Globalization;
+using System.Windows.Data;
+using TeamsISO.Engine.Domain;
+
+namespace TeamsISO.App.Converters;
+
+/// <summary>
+/// Renders engine enum values into operator-friendly strings.
+/// </summary>
+public sealed class EnumDescriptionConverter : IValueConverter
+{
+    public object? Convert(object? value, Type targetType, object? parameter, CultureInfo culture) => value switch
+    {
+        TargetFramerate fr => fr switch
+        {
+            TargetFramerate.Fps23_976 => "23.976 fps",
+            TargetFramerate.Fps24     => "24 fps",
+            TargetFramerate.Fps25     => "25 fps",
+            TargetFramerate.Fps29_97  => "29.97 fps",
+            TargetFramerate.Fps30     => "30 fps",
+            TargetFramerate.Fps50     => "50 fps",
+            TargetFramerate.Fps59_94  => "59.94 fps",
+            TargetFramerate.Fps60     => "60 fps",
+            _ => fr.ToString()
+        },
+        TargetResolution r => r switch
+        {
+            TargetResolution.R720p  => "720p",
+            TargetResolution.R1080p => "1080p",
+            TargetResolution.R4K    => "4K",
+            _ => r.ToString()
+        },
+        AspectMode a => a switch
+        {
+            AspectMode.Pillarbox => "Pillarbox",
+            AspectMode.Letterbox => "Letterbox",
+            AspectMode.Stretch   => "Stretch",
+            _ => a.ToString()
+        },
+        AudioMode m => m switch
+        {
+            AudioMode.Auto     => "Auto (isolated → mixed fallback)",
+            AudioMode.Isolated => "Isolated",
+            AudioMode.Mixed    => "Mixed",
+            _ => m.ToString()
+        },
+        _ => value
+    };
+
+    public object? ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture) =>
+        throw new NotSupportedException();
+}

src/TeamsISO.App/MainWindow.xaml

@@ -1,10 +1,159 @@
 <Window x:Class="TeamsISO.App.MainWindow"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-        Title="TeamsISO" Height="600" Width="900">
-    <Grid>
-        <TextBlock Text="TeamsISO — Phase A scaffold (UI implemented in Phase C)"
-                   HorizontalAlignment="Center" VerticalAlignment="Center"
-                   FontSize="16" Foreground="#444"/>
-    </Grid>
+        xmlns:vm="clr-namespace:TeamsISO.App.ViewModels"
+        xmlns:conv="clr-namespace:TeamsISO.App.Converters"
+        Title="TeamsISO" Height="700" Width="1100"
+        Background="#202225" Foreground="#E8E8E8">
+
+    <Window.Resources>
+        <conv:BoolToVisibilityConverter x:Key="BoolToVis" />
+        <conv:EnumDescriptionConverter x:Key="EnumDesc" />
+
+        <Style TargetType="TextBlock">
+            <Setter Property="Foreground" Value="#E8E8E8"/>
+            <Setter Property="FontFamily" Value="Segoe UI"/>
+            <Setter Property="FontSize" Value="13"/>
+        </Style>
+        <Style TargetType="Button">
+            <Setter Property="Padding" Value="10,4"/>
+            <Setter Property="Margin" Value="0,4,0,0"/>
+            <Setter Property="Background" Value="#3F4147"/>
+            <Setter Property="Foreground" Value="#E8E8E8"/>
+            <Setter Property="BorderBrush" Value="#5A5C63"/>
+        </Style>
+        <Style TargetType="ComboBox">
+            <Setter Property="Margin" Value="0,2,0,8"/>
+        </Style>
+    </Window.Resources>
+
+    <DockPanel>
+
+        <!-- Alert banner -->
+        <Border DockPanel.Dock="Top"
+                Background="#7A2B2B"
+                Padding="12,8"
+                Visibility="{Binding AlertBanner.IsVisible, Converter={StaticResource BoolToVis}}">
+            <DockPanel>
+                <Button DockPanel.Dock="Right"
+                        Content="Dismiss"
+                        Command="{Binding AlertBanner.DismissCommand}"
+                        Margin="12,0,0,0"/>
+                <TextBlock Text="{Binding AlertBanner.Message}"
+                           FontWeight="SemiBold"
+                           VerticalAlignment="Center"/>
+            </DockPanel>
+        </Border>
+
+        <!-- Status footer -->
+        <Border DockPanel.Dock="Bottom" Background="#191B1F" Padding="10,6">
+            <TextBlock Text="{Binding StatusText}" FontStyle="Italic" Foreground="#A0A0A0"/>
+        </Border>
+
+        <!-- Settings sidebar -->
+        <Border DockPanel.Dock="Right" Background="#2A2C32" Width="320" Padding="14">
+            <ScrollViewer VerticalScrollBarVisibility="Auto">
+                <StackPanel>
+                    <TextBlock Text="Global Settings" FontSize="16" FontWeight="Bold" Margin="0,0,0,12"/>
+
+                    <TextBlock Text="Target Framerate"/>
+                    <ComboBox ItemsSource="{Binding Settings.AvailableFramerates}"
+                              SelectedItem="{Binding Settings.Framerate}">
+                        <ComboBox.ItemTemplate>
+                            <DataTemplate>
+                                <TextBlock Text="{Binding Converter={StaticResource EnumDesc}}"/>
+                            </DataTemplate>
+                        </ComboBox.ItemTemplate>
+                    </ComboBox>
+
+                    <TextBlock Text="Target Resolution"/>
+                    <ComboBox ItemsSource="{Binding Settings.AvailableResolutions}"
+                              SelectedItem="{Binding Settings.Resolution}">
+                        <ComboBox.ItemTemplate>
+                            <DataTemplate>
+                                <TextBlock Text="{Binding Converter={StaticResource EnumDesc}}"/>
+                            </DataTemplate>
+                        </ComboBox.ItemTemplate>
+                    </ComboBox>
+
+                    <TextBlock Text="Aspect Mode"/>
+                    <ComboBox ItemsSource="{Binding Settings.AvailableAspectModes}"
+                              SelectedItem="{Binding Settings.Aspect}">
+                        <ComboBox.ItemTemplate>
+                            <DataTemplate>
+                                <TextBlock Text="{Binding Converter={StaticResource EnumDesc}}"/>
+                            </DataTemplate>
+                        </ComboBox.ItemTemplate>
+                    </ComboBox>
+
+                    <TextBlock Text="Audio Mode"/>
+                    <ComboBox ItemsSource="{Binding Settings.AvailableAudioModes}"
+                              SelectedItem="{Binding Settings.Audio}">
+                        <ComboBox.ItemTemplate>
+                            <DataTemplate>
+                                <TextBlock Text="{Binding Converter={StaticResource EnumDesc}}"/>
+                            </DataTemplate>
+                        </ComboBox.ItemTemplate>
+                    </ComboBox>
+
+                    <Button Content="Apply" Command="{Binding Settings.ApplyCommand}" Margin="0,16,0,0"/>
+                </StackPanel>
+            </ScrollViewer>
+        </Border>
+
+        <!-- Main content: participants list -->
+        <Grid Margin="14">
+            <Grid.RowDefinitions>
+                <RowDefinition Height="Auto"/>
+                <RowDefinition Height="*"/>
+            </Grid.RowDefinitions>
+
+            <TextBlock Grid.Row="0"
+                       Text="Participants"
+                       FontSize="16" FontWeight="Bold"
+                       Margin="0,0,0,8"/>
+
+            <DataGrid Grid.Row="1"
+                      ItemsSource="{Binding Participants}"
+                      AutoGenerateColumns="False"
+                      Background="#2A2C32"
+                      Foreground="#E8E8E8"
+                      RowBackground="#2A2C32"
+                      AlternatingRowBackground="#2E3037"
+                      BorderBrush="#5A5C63"
+                      GridLinesVisibility="Horizontal"
+                      HeadersVisibility="Column"
+                      CanUserAddRows="False" CanUserDeleteRows="False"
+                      RowHeight="34">
+                <DataGrid.Columns>
+                    <DataGridTextColumn Header="Display Name" Binding="{Binding DisplayName}" Width="2*" IsReadOnly="True"/>
+                    <DataGridTextColumn Header="Source" Binding="{Binding SourceMachine}" Width="*" IsReadOnly="True"/>
+                    <DataGridTextColumn Header="ISO Output Name" Binding="{Binding CustomName, UpdateSourceTrigger=PropertyChanged}" Width="2*"/>
+                    <DataGridTemplateColumn Header="ISO" Width="100">
+                        <DataGridTemplateColumn.CellTemplate>
+                            <DataTemplate>
+                                <Button Content="{Binding IsEnabled, StringFormat={}{0}}" Command="{Binding ToggleIsoCommand}">
+                                    <Button.Style>
+                                        <Style TargetType="Button">
+                                            <Setter Property="Content" Value="Enable"/>
+                                            <Style.Triggers>
+                                                <DataTrigger Binding="{Binding IsEnabled}" Value="True">
+                                                    <Setter Property="Content" Value="Disable"/>
+                                                    <Setter Property="Background" Value="#3D6F45"/>
+                                                </DataTrigger>
+                                                <DataTrigger Binding="{Binding IsProcessing}" Value="True">
+                                                    <Setter Property="Content" Value="…"/>
+                                                </DataTrigger>
+                                            </Style.Triggers>
+                                        </Style>
+                                    </Button.Style>
+                                </Button>
+                            </DataTemplate>
+                        </DataGridTemplateColumn.CellTemplate>
+                    </DataGridTemplateColumn>
+                </DataGrid.Columns>
+            </DataGrid>
+        </Grid>
+
+    </DockPanel>
 </Window>

src/TeamsISO.App/MainWindow.xaml.cs

@@ -1,4 +1,5 @@
 using System.Windows;
+using TeamsISO.App.ViewModels;
 
 namespace TeamsISO.App;
 
@@ -8,4 +9,9 @@ public partial class MainWindow : Window
     {
         InitializeComponent();
     }
+
+    public MainWindow(MainViewModel viewModel) : this()
+    {
+        DataContext = viewModel;
+    }
 }