feat(diff): persist diff view mode and wrap preference in ui config

tests/ClaudeDo.Ui.Tests/AppSettingsTests.cs

@@ -1,22 +1,68 @@
 using System.Text.Json;
 using ClaudeDo.Ui;
+using Xunit;
 
 namespace ClaudeDo.Ui.Tests;
 
 public class AppSettingsTests
 {
+    private static string TempConfigPath() =>
+        Path.Combine(Path.GetTempPath(), $"claudedo-uicfg-{Guid.NewGuid():N}.json");
+
     [Fact]
-    public void Language_defaults_to_empty()
+    public void DiffPreferences_DefaultToUnifiedAndNoWrap()
     {
-        Assert.Equal("", new AppSettings().Language);
+        var settings = new AppSettings();
+
+        Assert.Equal("unified", settings.DiffViewMode);
+        Assert.False(settings.DiffWrapLines);
     }
 
     [Fact]
-    public void Language_round_trips_through_json()
+    public void DiffPreferences_SurviveSaveAndLoad()
     {
-        var json = JsonSerializer.Serialize(new AppSettings { Language = "de" });
-        var back = JsonSerializer.Deserialize<AppSettings>(json,
+        var path = TempConfigPath();
+        try
+        {
+            new AppSettings { ConfigPath = path, DiffViewMode = "split", DiffWrapLines = true }.Save();
+
+            var restored = AppSettings.Load(path);
+
+            Assert.Equal("split", restored.DiffViewMode);
+            Assert.True(restored.DiffWrapLines);
+            Assert.Equal(path, restored.ConfigPath);
+        }
+        finally
+        {
+            if (File.Exists(path)) File.Delete(path);
+        }
+    }
+
+    [Fact]
+    public void ConfigPath_IsNotWrittenIntoTheConfigFile()
+    {
+        var path = TempConfigPath();
+        try
+        {
+            new AppSettings { ConfigPath = path }.Save();
+
+            Assert.DoesNotContain("ConfigPath", File.ReadAllText(path), StringComparison.OrdinalIgnoreCase);
+        }
+        finally
+        {
+            if (File.Exists(path)) File.Delete(path);
+        }
+    }
+
+    [Fact]
+    public void DiffPreferences_ReadFromCamelCasedConfig()
+    {
+        const string json = """{"diffViewMode":"split","diffWrapLines":true}""";
+
+        var restored = JsonSerializer.Deserialize<AppSettings>(json,
             new JsonSerializerOptions { PropertyNameCaseInsensitive = true })!;
-        Assert.Equal("de", back.Language);
+
+        Assert.Equal("split", restored.DiffViewMode);
+        Assert.True(restored.DiffWrapLines);
     }
 }