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.Tests/ViewModels/GroupEditViewModelTests.cs

@@ -26,12 +26,32 @@ public class GroupEditViewModelTests
     }
 
     [Fact]
-    public void Constructor_AddMode_LoadsOnlyNonGroupTools()
+    public void Constructor_AddMode_LoadsAllToolsIncludingGroups()
     {
         var vm = new GroupEditViewModel(_dataServiceMock.Object, _logServiceMock.Object);
 
         Assert.Equal("添加组合", vm.WindowTitle);
-        Assert.Equal(2, vm.AvailableTools.Count); // t1, t2 only (t3 is a group)
+        Assert.Equal(3, vm.AvailableTools.Count); // t1, t2, t3 (new groups can include other groups)
+    }
+
+    [Fact]
+    public void Constructor_EditMode_ExcludesSelfAndAncestors()
+    {
+        // Group A (t3) contains t1 -> Group B being edited should exclude itself
+        var group = new ToolItem
+        {
+            Id = "t4",
+            Name = "GroupB",
+            IsGroup = true,
+            SubToolIds = new List<string>()
+        };
+        // t3 contains t4, so t3 is an ancestor of t4
+        _config.Tools.First(t => t.Id == "t3").SubToolIds.Add("t4");
+
+        var vm = new GroupEditViewModel(_dataServiceMock.Object, _logServiceMock.Object, group);
+
+        // t4 (self) and t3 (ancestor) should be excluded
+        Assert.Equal(2, vm.AvailableTools.Count); // t1, t2 only
     }
 
     [Fact]