feat: 实现 Task 6-7 报告和存储服务

Task 6 - 转换报告:
- 扩展 ConversionReport 模型
- 添加 Id, ProjectId, SourceLanguage, TargetLanguage
- 添加 IssueCount, TodoCount, ValidationStatus
- 添加 CreatedAt, LastValidatedAt 时间戳

Task 7 - 存储服务:
- IReportStorageService 接口
- ReportStorageService 内存实现 (MVP 版)
- 支持保存/查询/删除报告
- 项目统计功能

WebAPI 项目:
- CodePlay.WebAPI 项目创建
- JWT 认证配置
- AuthController (login, refresh, me)
- ReportController (CRUD + stats)
- Swagger 集成

测试：39 个测试全部通过 ✅
Co-authored-by: monkeycode-ai <monkeycode-ai@chaitin.com>

CodePlay.Core/Models/ConversionModels.cs

@@ -115,6 +115,26 @@ public class ConversionResult
 /// </summary>
 public class ConversionReport
 {
+    /// <summary>
+    /// 报告 ID
+    /// </summary>
+    public string Id { get; set; } = Guid.NewGuid().ToString("N")[..20];
+    
+    /// <summary>
+    /// 项目 ID
+    /// </summary>
+    public string ProjectId { get; set; } = string.Empty;
+    
+    /// <summary>
+    /// 源语言
+    /// </summary>
+    public LanguageType SourceLanguage { get; set; }
+    
+    /// <summary>
+    /// 目标语言
+    /// </summary>
+    public LanguageType TargetLanguage { get; set; }
+    
     /// <summary>
     /// 转换的行数
     /// </summary>
@@ -135,6 +155,16 @@ public class ConversionReport
     /// </summary>
     public TimeSpan Duration { get; set; }
     
+    /// <summary>
+    /// 问题数量
+    /// </summary>
+    public int IssueCount { get; set; }
+    
+    /// <summary>
+    /// TODO 数量
+    /// </summary>
+    public int TodoCount { get; set; }
+    
     /// <summary>
     /// 问题列表
     /// </summary>
@@ -149,6 +179,21 @@ public class ConversionReport
     /// TODO 列表
     /// </summary>
     public List<TodoItem> TodoItems { get; set; } = new();
+    
+    /// <summary>
+    /// 验证状态
+    /// </summary>
+    public string ValidationStatus { get; set; } = "NotValidated";
+    
+    /// <summary>
+    /// 最后验证时间
+    /// </summary>
+    public DateTime? LastValidatedAt { get; set; }
+    
+    /// <summary>
+    /// 创建时间
+    /// </summary>
+    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
 }
 
 /// <summary>