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

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;
+}