Phase 2-3: UI layout, theme switching, CRUD tools, process execution

- Phase 2: MainWindow 3-section layout (sidebar/content/log bar), Dark/Light theme with ThemeHelper, MainViewModel with ObservableProperty/RelayCommand, tool card filtering by search + category

- Phase 3: ToolEditWindow for add/edit tools, ProcessExecutionService (Process.Start + error handling), double-click + right-click context menu (run/edit), path browse dialog

- Bugfix: ContextMenu commands now use PlacementTarget.Tag binding (ContextMenu in separate visual tree)

- Bugfix: StaticResource converters moved to XAML before DataTemplate to fix XamlParseException on tool card render

- Bugfix: Pure filenames (no path separators) treated as PATH commands, not marked invalid

- Bugfix: RefreshData preserves SelectedCategory; Load() catches all exceptions; Save() wrapped in try-catch; auto-scroll log to newest entry

- Tests: xUnit project with 55 tests covering models, services, converters, and view models

PersonalToolBox.Tests/Models/ModelSerializationTests.cs

@@ -0,0 +1,118 @@
+using System.Text.Json;
+using PersonalToolBox.Models;
+
+namespace PersonalToolBox.Tests.Models;
+
+public class ModelSerializationTests
+{
+    private static readonly JsonSerializerOptions Options = new()
+    {
+        WriteIndented = true,
+        PropertyNameCaseInsensitive = true
+    };
+
+    [Fact]
+    public void AppConfig_Serialize_ProducesValidJson()
+    {
+        var config = new AppConfig
+        {
+            Theme = "Dark",
+            AutoStart = true,
+            Categories =
+            [
+                new() { Id = "1", Name = "开发工具" },
+                new() { Id = "2", Name = "常用脚本" }
+            ],
+            Tools =
+            [
+                new()
+                {
+                    Id = "tool-1",
+                    Name = "Postman",
+                    IconCode = "f0c2",
+                    ExecutablePath = @"D:\tools\postman.exe",
+                    Arguments = "",
+                    CategoryId = "1",
+                    HotKey = "Ctrl+Alt+P"
+                }
+            ]
+        };
+
+        var json = JsonSerializer.Serialize(config, Options);
+        var deserialized = JsonSerializer.Deserialize<AppConfig>(json, Options);
+
+        Assert.NotNull(deserialized);
+        Assert.Equal("Dark", deserialized.Theme);
+        Assert.True(deserialized.AutoStart);
+        Assert.Equal(2, deserialized.Categories.Count);
+        Assert.Single(deserialized.Tools);
+    }
+
+    [Fact]
+    public void ToolItem_IsValid_NotIncludedInJson()
+    {
+        var tool = new ToolItem
+        {
+            Name = "TestTool",
+            ExecutablePath = @"C:\nonexistent.exe",
+            IsValid = false
+        };
+
+        var json = JsonSerializer.Serialize(tool, Options);
+
+        Assert.DoesNotContain("IsValid", json);
+    }
+
+    [Fact]
+    public void ToolItem_DefaultValues_AreCorrect()
+    {
+        var tool = new ToolItem();
+
+        Assert.NotEmpty(tool.Id);
+        Assert.Empty(tool.Name);
+        Assert.True(tool.IsValid);
+    }
+
+    [Fact]
+    public void Category_DefaultId_IsNotEmpty()
+    {
+        var cat = new Category();
+        Assert.NotEmpty(cat.Id);
+    }
+
+    [Fact]
+    public void AppConfig_DefaultValues_AreCorrect()
+    {
+        var config = new AppConfig();
+
+        Assert.Equal("Dark", config.Theme);
+        Assert.False(config.AutoStart);
+        Assert.NotNull(config.Categories);
+        Assert.NotNull(config.Tools);
+        Assert.Empty(config.Categories);
+        Assert.Empty(config.Tools);
+    }
+
+    [Fact]
+    public void Deserialize_EmptyJson_ProducesValidConfig()
+    {
+        var json = "{}";
+        var config = JsonSerializer.Deserialize<AppConfig>(json, Options);
+
+        Assert.NotNull(config);
+        Assert.Equal("Dark", config.Theme);
+        Assert.False(config.AutoStart);
+        Assert.Empty(config.Categories);
+        Assert.Empty(config.Tools);
+    }
+
+    [Fact]
+    public void Deserialize_WithUnknownProperty_IgnoresIt()
+    {
+        var json = """{"unknownField": 123, "Theme": "Light"}""";
+        var config = JsonSerializer.Deserialize<AppConfig>(json, Options);
+
+        Assert.NotNull(config);
+        Assert.Equal("Light", config.Theme);
+    }
+}