refactor: 重构项目基础架构与实体体系

- 替换原有自定义生命周期接口为通用基础服务体系
- 将所有实体基类替换为带雪花ID的SqlSugarBaseEntity
- 迁移DTO到Models项目并统一管理
- 移除冗余的Repository层实现，改用通用基础服务
- 添加Yitter.IdGenerator雪花ID生成支持
- 重构SqlSugar数据库上下文与依赖注入配置
- 新增微信用户、用户勋章、背包等实体与配套服务
- 整理分页查询与结果封装类
- 优化WebApi控制器结构

QYZH.InteractiveMagazine.Common/Helpers/JsonConverterUtil.cs

@@ -0,0 +1,37 @@
+using System;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace QYZH.InteractiveMagazine.Common.Helpers
+{
+    public class JsonConverterUtil
+    {
+        public class DateTimeNullConverter : JsonConverter<DateTime?>
+        {
+            public override DateTime? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+                => string.IsNullOrEmpty(reader.GetString()) ? default : ParseDateTime(reader.GetString());
+
+            public override void Write(Utf8JsonWriter writer, DateTime? value, JsonSerializerOptions options)
+                => writer.WriteStringValue(value?.ToString("yyyy-MM-dd HH:mm:ss"));
+        }
+
+        public class DateTimeConverter : JsonConverter<DateTime>
+        {
+            public override DateTime Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+            {
+                var dateTime = ParseDateTime(reader.GetString());
+                return dateTime == null ? DateTime.MinValue : dateTime.Value;
+            }
+
+            public override void Write(Utf8JsonWriter writer, DateTime value, JsonSerializerOptions options)
+                => writer.WriteStringValue(value.ToString("yyyy-MM-dd HH:mm:ss"));
+        }
+
+        public static DateTime? ParseDateTime(string dateStr)
+        {
+            if (System.Text.RegularExpressions.Regex.IsMatch(dateStr, @"^\d{4}[/-]") && DateTime.TryParse(dateStr, null, System.Globalization.DateTimeStyles.AssumeLocal, out var dateVal))
+                return dateVal;
+            return null;
+        }
+    }
+}