Phase 1: data models and local storage service

- Add Models: Category, ToolItem (IsValid runtime-only, not stored), AppConfig

- Add Services: IDataService + JsonDataService (JSON load/save)

- Path validation on Load(): File.Exists check, logs warning for missing paths

- Startup: auto-calls dataService.Load() to load config

PersonalToolBox/Models/Category.cs

@@ -0,0 +1,17 @@
+namespace PersonalToolBox.Models;
+
+/// <summary>
+/// 工具标签页分类
+/// </summary>
+public class Category
+{
+    /// <summary>
+    /// 分类唯一标识
+    /// </summary>
+    public string Id { get; set; } = Guid.NewGuid().ToString();
+
+    /// <summary>
+    /// 分类显示名称（如：开发工具、常用脚本）
+    /// </summary>
+    public string Name { get; set; } = string.Empty;
+}