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/Services/LogServiceTests.cs

@@ -0,0 +1,96 @@
+using PersonalToolBox.Models;
+using PersonalToolBox.Services;
+
+namespace PersonalToolBox.Tests.Services;
+
+public class LogServiceTests
+{
+    private readonly LogService _logService = new();
+
+    [Fact]
+    public void Info_AddsLogEntry()
+    {
+        _logService.Info("test message");
+
+        Assert.Single(_logService.Logs);
+        var entry = _logService.Logs[0];
+        Assert.Equal(LogLevel.Info, entry.Level);
+        Assert.Equal("test message", entry.Content);
+        Assert.True((DateTime.Now - entry.Timestamp).TotalSeconds < 2);
+    }
+
+    [Fact]
+    public void Warning_AddsLogEntry_WithWarningLevel()
+    {
+        _logService.Warning("disk full");
+
+        Assert.Single(_logService.Logs);
+        Assert.Equal(LogLevel.Warning, _logService.Logs[0].Level);
+        Assert.Equal("disk full", _logService.Logs[0].Content);
+    }
+
+    [Fact]
+    public void Error_AddsLogEntry_WithErrorLevel()
+    {
+        _logService.Error("crash detected");
+
+        Assert.Single(_logService.Logs);
+        Assert.Equal(LogLevel.Error, _logService.Logs[0].Level);
+        Assert.Equal("crash detected", _logService.Logs[0].Content);
+    }
+
+    [Fact]
+    public void MultipleLogs_AreAddedInOrder()
+    {
+        _logService.Info("first");
+        _logService.Warning("second");
+        _logService.Error("third");
+
+        Assert.Equal(3, _logService.Logs.Count);
+        Assert.Equal(LogLevel.Info, _logService.Logs[0].Level);
+        Assert.Equal(LogLevel.Warning, _logService.Logs[1].Level);
+        Assert.Equal(LogLevel.Error, _logService.Logs[2].Level);
+    }
+
+    [Fact]
+    public void Clear_RemovesAllEntries()
+    {
+        _logService.Info("msg");
+        _logService.Info("msg");
+
+        Assert.Equal(2, _logService.Logs.Count);
+
+        _logService.Clear();
+
+        Assert.Empty(_logService.Logs);
+    }
+
+    [Fact]
+    public void LogEntry_ToString_FormatsCorrectly()
+    {
+        var entry = new LogEntry
+        {
+            Timestamp = new DateTime(2026, 5, 9, 20, 0, 0),
+            Level = LogLevel.Warning,
+            Content = "path not found"
+        };
+
+        var str = entry.ToString();
+
+        Assert.Contains("[2026-05-09 20:00:00]", str);
+        Assert.Contains("[警告]", str);
+        Assert.Contains("path not found", str);
+    }
+
+    [Fact]
+    public void LogEntry_LevelText_ProducesChineseLabels()
+    {
+        var info = new LogEntry { Level = LogLevel.Info };
+        var warn = new LogEntry { Level = LogLevel.Warning };
+        var err = new LogEntry { Level = LogLevel.Error };
+
+        Assert.Equal("[信息]", info.LevelText);
+        Assert.Equal("[警告]", warn.LevelText);
+        Assert.Equal("[错误]", err.LevelText);
+    }
+}