feat(i18n): add Avalonia loc:Tr markup extension and LocalizedString

src/ClaudeDo.Ui/ClaudeDo.Ui.csproj

@@ -2,6 +2,7 @@
 
   <ItemGroup>
     <ProjectReference Include="..\ClaudeDo.Data\ClaudeDo.Data.csproj" />
+    <ProjectReference Include="..\ClaudeDo.Localization\ClaudeDo.Localization.csproj" />
     <ProjectReference Include="..\ClaudeDo.Releases\ClaudeDo.Releases.csproj" />
   </ItemGroup>
 

src/ClaudeDo.Ui/Localization/LocalizedString.cs

@@ -0,0 +1,22 @@
+using System.ComponentModel;
+using ClaudeDo.Localization;
+
+namespace ClaudeDo.Ui.Localization;
+
+public sealed class LocalizedString : INotifyPropertyChanged
+{
+    private readonly ILocalizer _localizer;
+    private readonly string _key;
+
+    public LocalizedString(ILocalizer localizer, string key)
+    {
+        _localizer = localizer;
+        _key = key;
+        _localizer.LanguageChanged += (_, _) =>
+            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Value)));
+    }
+
+    public string Value => _localizer[_key];
+
+    public event PropertyChangedEventHandler? PropertyChanged;
+}

src/ClaudeDo.Ui/Localization/TrExtension.cs

@@ -0,0 +1,25 @@
+using Avalonia.Data;
+using Avalonia.Markup.Xaml;
+using ClaudeDo.Localization;
+
+namespace ClaudeDo.Ui.Localization;
+
+public sealed class TrExtension : MarkupExtension
+{
+    public TrExtension() { }
+    public TrExtension(string key) => Key = key;
+
+    public string Key { get; set; } = "";
+
+    public static ILocalizer? Localizer { get; set; }
+
+    public override object ProvideValue(IServiceProvider serviceProvider)
+    {
+        var loc = Localizer ?? throw new InvalidOperationException("TrExtension.Localizer not initialized");
+        return new Binding(nameof(LocalizedString.Value))
+        {
+            Source = new LocalizedString(loc, Key),
+            Mode = BindingMode.OneWay
+        };
+    }
+}