feat(ui): complete Avalonia UI port with 7 main pages, tool settings & top MenuBar

src/ClawdDotNet.Desktop/Views/LicenseWindow.axaml

@@ -0,0 +1,45 @@
+<Window xmlns="https://github.com/avaloniaui"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+        xmlns:vm="using:ClawdDotNet.Desktop.ViewModels"
+        mc:Ignorable="d" d:DesignWidth="520" d:DesignHeight="320"
+        x:Class="ClawdDotNet.Desktop.Views.LicenseWindow"
+        x:DataType="vm:LicenseViewModel"
+        Icon="/Assets/app.ico"
+        Title="ClawdDotNet – Lizenz"
+        Width="520" SizeToContent="Height"
+        CanResize="False"
+        WindowStartupLocation="CenterScreen">
+
+  <StackPanel Margin="20" Spacing="12">
+
+    <TextBlock Classes="heading" Text="Lizenzschlüssel" />
+
+    <!-- Nur sichtbar, wenn es einen Grund gibt -->
+    <Border Classes="card"
+            IsVisible="{Binding Problem, Converter={x:Static StringConverters.IsNotNullOrEmpty}}">
+      <TextBlock Text="{Binding Problem}" TextWrapping="Wrap"
+                 Foreground="{DynamicResource SystemFillColorCriticalBrush}" />
+    </Border>
+
+    <TextBox Watermark="XXXXX-XXXXX-XXXXX-XXXXX-XXXXX"
+             Text="{Binding Key}"
+             FontFamily="{DynamicResource ContentControlThemeFontFamily}" />
+
+    <StackPanel Spacing="4">
+      <TextBlock Classes="caption" Text="Hardware-ID (für den Support):" />
+      <SelectableTextBlock Classes="caption"
+                           Text="{Binding HardwareId}"
+                           TextWrapping="Wrap" />
+    </StackPanel>
+
+    <StackPanel Orientation="Horizontal" Spacing="8" HorizontalAlignment="Right">
+      <Button Content="Beenden" Command="{Binding CancelCommand}" />
+      <Button Content="Prüfen" Classes="accent" IsDefault="True"
+              Command="{Binding ConfirmCommand}" />
+    </StackPanel>
+
+  </StackPanel>
+
+</Window>