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/Services/IProcessExecutionService.cs

@@ -0,0 +1,15 @@
+using PersonalToolBox.Models;
+
+namespace PersonalToolBox.Services;
+
+/// <summary>
+/// 进程执行服务接口，负责启动外部工具进程
+/// </summary>
+public interface IProcessExecutionService
+{
+    /// <summary>
+    /// 执行指定的工具项
+    /// </summary>
+    /// <param name="tool">要执行的工具项</param>
+    void Execute(ToolItem tool);
+}