Replace default Avalonia about dialog with Conclave-branded modal

src/Conclave.App/MainWindow.axaml

@@ -8,6 +8,14 @@
         Icon="/Assets/icon.png"
         Width="1320" Height="820" MinWidth="640" MinHeight="480"
         Background="{Binding Tokens.Bg}">
+    <!-- macOS app menu: replaces Avalonia's default "About Avalonia" item with our
+         own Conclave-branded modal. On Windows/Linux this attached menu is unused
+         (no menu bar is rendered). -->
+    <NativeMenu.Menu>
+        <NativeMenu>
+            <NativeMenuItem Header="About Conclave" Click="OnAboutMenuClick" />
+        </NativeMenu>
+    </NativeMenu.Menu>
     <Panel>
         <!-- Five-column layout: sidebar · splitter · main · splitter · right.
              Sidebar and right widths are pixel-sized and user-resizable via the
@@ -64,6 +72,7 @@
         <shell:NewSessionModal />
         <shell:NewFusionProjectModal />
         <shell:PreferencesModal />
+        <shell:AboutModal />
         <shell:Toast />
     </Panel>
 </Window>

src/Conclave.App/MainWindow.axaml.cs

@@ -138,4 +138,6 @@ private void ApplyResponsiveLayout(double windowWidth, bool hasActiveSession)
     }
 
     private bool RightColIsZero() => RightCol.Width.Value == 0;
+
+    private void OnAboutMenuClick(object? sender, System.EventArgs e) => _shell?.OpenAbout();
 }

src/Conclave.App/ViewModels/ShellVm.cs

@@ -1,5 +1,6 @@
 using System.Collections.ObjectModel;
 using System.Collections.Specialized;
+using System.Reflection;
 using Conclave.App.Claude;
 using Conclave.App.Design;
 using Conclave.App.Sessions;
@@ -119,6 +120,36 @@ public bool IsPreferencesOpen
     public void OpenPreferences() => IsPreferencesOpen = true;
     public void ClosePreferences() => IsPreferencesOpen = false;
 
+    // --- About ---
+
+    private bool _isAboutOpen;
+    public bool IsAboutOpen
+    {
+        get => _isAboutOpen;
+        set => Set(ref _isAboutOpen, value);
+    }
+
+    public void OpenAbout() => IsAboutOpen = true;
+    public void CloseAbout() => IsAboutOpen = false;
+
+    // Reads the assembly's InformationalVersion (stamped by `dotnet publish -p:Version=...`)
+    // and trims the trailing `+commit` build metadata SourceLink appends. Falls back to the
+    // numeric assembly version, then a dev sentinel.
+    public string AppVersion
+    {
+        get
+        {
+            var asm = typeof(ShellVm).Assembly;
+            var info = asm.GetCustomAttribute<AssemblyInformationalVersionAttribute>()?.InformationalVersion;
+            if (!string.IsNullOrEmpty(info))
+            {
+                var plus = info.IndexOf('+');
+                return plus >= 0 ? info[..plus] : info;
+            }
+            return asm.GetName().Version?.ToString() ?? "0.0.0-dev";
+        }
+    }
+
     public bool AutoCleanupEnabled
     {
         get => SettingsKeys.ReadAutoCleanupEnabled(Manager.Db);

src/Conclave.App/Views/Shell/AboutModal.axaml

@@ -0,0 +1,57 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:vm="clr-namespace:Conclave.App.ViewModels"
+             x:Class="Conclave.App.Views.Shell.AboutModal"
+             x:DataType="vm:ShellVm">
+    <Panel IsVisible="{Binding IsAboutOpen}" IsHitTestVisible="{Binding IsAboutOpen}"
+           KeyDown="OnModalKeyDown"
+           Focusable="True">
+        <Border Background="#A6000000" PointerPressed="OnBackdropPressed" />
+
+        <Border Width="420"
+                VerticalAlignment="Center" HorizontalAlignment="Center"
+                Background="{Binding Tokens.Bg}"
+                BorderBrush="{Binding Tokens.BorderHi}" BorderThickness="1"
+                CornerRadius="{Binding Tokens.RadLgCorner}"
+                Padding="32,28">
+            <Border.Effect>
+                <DropShadowEffect BlurRadius="60" OffsetY="20" Opacity="0.5" Color="Black" />
+            </Border.Effect>
+
+            <StackPanel Spacing="10" HorizontalAlignment="Center">
+                <Image Source="avares://Conclave.App/Assets/icon.png"
+                       Width="72" Height="72"
+                       HorizontalAlignment="Center" Margin="0,0,0,4" />
+
+                <TextBlock Text="Conclave" FontSize="22" FontWeight="SemiBold"
+                           Foreground="{Binding Tokens.Text}"
+                           HorizontalAlignment="Center" />
+
+                <TextBlock Text="{Binding AppVersion, StringFormat='Version {0}'}"
+                           FontSize="11.5" Foreground="{Binding Tokens.TextDim}"
+                           FontFamily="ui-monospace,SFMono-Regular,Menlo,monospace"
+                           HorizontalAlignment="Center" />
+
+                <TextBlock Text="A desktop home for your Claude Code sessions — many at once, each in its own git worktree."
+                           FontSize="12" Foreground="{Binding Tokens.TextDim}"
+                           TextWrapping="Wrap" TextAlignment="Center"
+                           Margin="8,8,8,0" />
+
+                <TextBlock Text="github.com/Cellcote/Conclave"
+                           FontSize="11" Foreground="{Binding Tokens.TextMute}"
+                           FontFamily="ui-monospace,SFMono-Regular,Menlo,monospace"
+                           HorizontalAlignment="Center" Margin="0,8,0,0" />
+
+                <TextBlock Text="MIT License · © 2026 Rik Schreurs"
+                           FontSize="11" Foreground="{Binding Tokens.TextMute}"
+                           HorizontalAlignment="Center" />
+
+                <Button Content="Done" Click="OnDone"
+                        Background="{Binding Tokens.Text}" BorderThickness="0"
+                        CornerRadius="{Binding Tokens.RadSmCorner}" Padding="18,5"
+                        Foreground="{Binding Tokens.Bg}" FontSize="12" FontWeight="SemiBold"
+                        HorizontalAlignment="Center" Margin="0,16,0,0" />
+            </StackPanel>
+        </Border>
+    </Panel>
+</UserControl>

src/Conclave.App/Views/Shell/AboutModal.axaml.cs

@@ -0,0 +1,34 @@
+using Avalonia.Controls;
+using Avalonia.Input;
+using Avalonia.Interactivity;
+using Avalonia.Markup.Xaml;
+using Conclave.App.ViewModels;
+
+namespace Conclave.App.Views.Shell;
+
+public partial class AboutModal : UserControl
+{
+    public AboutModal() => InitializeComponent();
+
+    private void OnBackdropPressed(object? sender, PointerPressedEventArgs e)
+    {
+        if (DataContext is ShellVm shell) shell.CloseAbout();
+    }
+
+    private void OnDone(object? sender, RoutedEventArgs e)
+    {
+        if (DataContext is ShellVm shell) shell.CloseAbout();
+    }
+
+    private void OnModalKeyDown(object? sender, KeyEventArgs e)
+    {
+        if (DataContext is not ShellVm shell || !shell.IsAboutOpen) return;
+        if (e.Key == Key.Escape)
+        {
+            shell.CloseAbout();
+            e.Handled = true;
+        }
+    }
+
+    private void InitializeComponent() => AvaloniaXamlLoader.Load(this);
+}