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

src/ClaudeDo.Ui/AppSettings.cs

@@ -1,4 +1,5 @@
 using System.Text.Json;
+using System.Text.Json.Serialization;
 using ClaudeDo.Data;
 
 namespace ClaudeDo.Ui;
@@ -10,24 +11,40 @@ public sealed class AppSettings
     public string Language { get; set; } = "";
     public string AccentPreset { get; set; } = "";
 
-    private static readonly string ConfigPath = Paths.Expand("~/.todo-app/ui.config.json");
+    /// Diff viewer layout: "unified" or "split". A view preference, so it lives here in
+    /// ui.config.json rather than in the worker-owned AppSettingsEntity.
+    public string DiffViewMode { get; set; } = "unified";
+    public bool DiffWrapLines { get; set; }
 
-    public static AppSettings Load()
+    private static readonly string DefaultConfigPath = Paths.Expand("~/.todo-app/ui.config.json");
+
+    /// Where this instance persists. Instance-level (not static) so tests can redirect it —
+    /// the diff-viewer toggles call Save() on every flip.
+    [JsonIgnore]
+    public string ConfigPath { get; set; } = DefaultConfigPath;
+
+    public static AppSettings Load(string? configPath = null)
     {
+        var path = configPath ?? DefaultConfigPath;
         try
         {
-            if (File.Exists(ConfigPath))
+            if (File.Exists(path))
             {
-                var json = File.ReadAllText(ConfigPath);
-                return JsonSerializer.Deserialize<AppSettings>(json,
-                    new JsonSerializerOptions { PropertyNameCaseInsensitive = true }) ?? new();
+                var json = File.ReadAllText(path);
+                var loaded = JsonSerializer.Deserialize<AppSettings>(json,
+                    new JsonSerializerOptions { PropertyNameCaseInsensitive = true });
+                if (loaded is not null)
+                {
+                    loaded.ConfigPath = path;
+                    return loaded;
+                }
             }
         }
         catch
         {
             // Fall through to defaults
         }
-        return new();
+        return new AppSettings { ConfigPath = path };
     }
 
     public void Save()