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/Services/IDataService.cs

@@ -0,0 +1,24 @@
+using PersonalToolBox.Models;
+
+namespace PersonalToolBox.Services;
+
+/// <summary>
+/// 数据持久化服务接口，负责配置的加载和保存
+/// </summary>
+public interface IDataService
+{
+    /// <summary>
+    /// 当前加载的配置数据
+    /// </summary>
+    AppConfig Config { get; }
+
+    /// <summary>
+    /// 从 config.json 加载配置，验证工具路径有效性
+    /// </summary>
+    void Load();
+
+    /// <summary>
+    /// 保存当前配置到 config.json
+    /// </summary>
+    void Save();
+}