Phase 7: 自定义图标系统 + 组合嵌套 + 删除功能 + UI 优化

- 安装 FontAwesome.Sharp v6.6.0，新增 Helpers/IconProvider.cs（190+ 图标，11 分类）
- ToolEditWindow/GroupEditWindow: 添加图标选择 ComboBox，按分类分组，带图标预览
- MainWindow 卡片模板: 使用 fa:IconBlock 渲染图标，IconCode 为空时回退首字母
- 组合角标从 emoji 改为 FontAwesome Cubes 图标，放置于卡片右上角
- ComboBox 样式修复: TextBlock→ContentPresenter，支持 ItemTemplate+DisplayMemberPath
- ComboBox 滚轮修复: CanContentScroll=False 解决分组模式下滑轮跳组问题
- 编辑弹窗: 所有输入控件添加 VerticalContentAlignment=Center
- 组合可包含其他组合: GetAncestorIds 递归排除自身及祖先防止循环引用
- ProcessExecutionService: 支持嵌套组合递归执行，visited 集合防死循环
- MainWindow 右键菜单新增删除功能，工具和组合均支持
- 移除侧边栏顶部个人工具箱标题文字
- 更新测试: 适配组合嵌套逻辑，新增祖先排除测试 (83/83 通过)

PersonalToolBox/ViewModels/ToolEditViewModel.cs

@@ -1,9 +1,11 @@
 using System.Collections.ObjectModel;
+using System.ComponentModel;
 using System.IO;
 using System.Linq;
 using CommunityToolkit.Mvvm.ComponentModel;
 using CommunityToolkit.Mvvm.Input;
 using Microsoft.Win32;
+using PersonalToolBox.Helpers;
 using PersonalToolBox.Models;
 using PersonalToolBox.Services;
 
@@ -38,11 +40,19 @@ public partial class ToolEditViewModel : ObservableObject
     [ObservableProperty]
     private Category? _selectedCategory;
 
+    [ObservableProperty]
+    private IconProvider.IconOption? _selectedIcon;
+
     /// <summary>
     /// 分类下拉列表
     /// </summary>
     public ObservableCollection<Category> Categories { get; } = new();
 
+    /// <summary>
+    /// 按分类分组的可用图标列表
+    /// </summary>
+    public ListCollectionView AvailableIconsView { get; }
+
     /// <summary>
     /// 窗口关闭回调（由 View 层设置）
     /// </summary>
@@ -61,6 +71,9 @@ public partial class ToolEditViewModel : ObservableObject
         _logService = logService;
         _editingTool = toolToEdit;
 
+        AvailableIconsView = new ListCollectionView(IconProvider.AvailableIcons);
+        AvailableIconsView.GroupDescriptions.Add(new PropertyGroupDescription("Category"));
+
         // 加载分类列表
         foreach (var cat in _dataService.Config.Categories)
             Categories.Add(cat);
@@ -74,6 +87,11 @@ public partial class ToolEditViewModel : ObservableObject
             Arguments = toolToEdit.Arguments;
             HotKey = toolToEdit.HotKey;
             SelectedCategory = Categories.FirstOrDefault(c => c.Id == toolToEdit.CategoryId);
+
+            if (!string.IsNullOrEmpty(toolToEdit.IconCode))
+            {
+                SelectedIcon = IconProvider.AvailableIcons.FirstOrDefault(i => i.Icon.ToString() == toolToEdit.IconCode);
+            }
         }
     }
 
@@ -125,6 +143,7 @@ public partial class ToolEditViewModel : ObservableObject
             if (_editingTool != null)
             {
                 _editingTool.Name = Name.Trim();
+                _editingTool.IconCode = SelectedIcon?.Icon.ToString() ?? string.Empty;
                 _editingTool.ExecutablePath = ExecutablePath.Trim();
                 _editingTool.Arguments = Arguments.Trim();
                 _editingTool.HotKey = HotKey.Trim();
@@ -139,6 +158,7 @@ public partial class ToolEditViewModel : ObservableObject
                 var newTool = new ToolItem
                 {
                     Name = Name.Trim(),
+                    IconCode = SelectedIcon?.Icon.ToString() ?? string.Empty,
                     ExecutablePath = ExecutablePath.Trim(),
                     Arguments = Arguments.Trim(),
                     HotKey = HotKey.Trim(),