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/ProcessExecutionService.cs

@@ -0,0 +1,49 @@
+using System.Diagnostics;
+using PersonalToolBox.Models;
+
+namespace PersonalToolBox.Services;
+
+/// <summary>
+/// 进程执行服务，负责启动外部工具进程并处理异常
+/// </summary>
+public class ProcessExecutionService : IProcessExecutionService
+{
+    private readonly ILogService _logService;
+
+    public ProcessExecutionService(ILogService logService)
+    {
+        _logService = logService;
+    }
+
+    public void Execute(ToolItem tool)
+    {
+        if (tool == null)
+        {
+            _logService.Error("尝试执行空工具项");
+            return;
+        }
+
+        if (!tool.IsValid)
+        {
+            _logService.Warning($"无法运行工具 \"{tool.Name}\"，路径失效: {tool.ExecutablePath}");
+            return;
+        }
+
+        try
+        {
+            var startInfo = new ProcessStartInfo
+            {
+                FileName = tool.ExecutablePath,
+                Arguments = tool.Arguments ?? string.Empty,
+                UseShellExecute = true
+            };
+
+            Process.Start(startInfo);
+            _logService.Info($"成功启动: {tool.Name}");
+        }
+        catch (Exception ex)
+        {
+            _logService.Error($"启动工具 \"{tool.Name}\" 失败: {ex.Message}");
+        }
+    }
+}