feat: 后端架构重构 — Endpoint→Service→Repository分层 + AI确认机制 + 异步任务持久化

- 核心业务拆分为 Endpoint → Application Service → Repository 三层
- AI写入操作必须用户确认后才写库(确认卡片机制)
- 报告/饮食/用药分析改为持久化任务队列(原子领取/重试/重启恢复)
- 运动计划修复: 连续真实日期替代周模板
- 用药提醒去重 + 通知Outbox预留
- 认证收拢到AuthService, 管理员收拢到AdminService
- AI会话加用户归属校验防串号
- 提示词调整为患者视角
- 开发假数据已关闭
- 21/21测试通过, 0警告0错误

backend/src/Health.Application/Notifications/InAppNotificationContracts.cs

@@ -0,0 +1,26 @@
+namespace Health.Application.Notifications;
+
+public sealed record InAppNotificationDto(
+    Guid Id,
+    string Type,
+    string Title,
+    string Message,
+    DateTime CreatedAt);
+
+public interface IInAppNotificationService
+{
+    Task<IReadOnlyList<InAppNotificationDto>> GetPendingAsync(Guid userId, CancellationToken ct);
+    Task<bool> AcknowledgeAsync(Guid userId, Guid notificationId, CancellationToken ct);
+}
+
+public interface IInAppNotificationRepository
+{
+    Task<IReadOnlyList<InAppNotificationRecord>> GetPendingAsync(Guid userId, CancellationToken ct);
+    Task<bool> AcknowledgeAsync(Guid userId, Guid notificationId, CancellationToken ct);
+}
+
+public sealed record InAppNotificationRecord(
+    Guid Id,
+    string Type,
+    string Payload,
+    DateTime CreatedAt);