chore: 全面规范化代码，遵循 CLAUDE.md 编码规范

- C# 文件命名改为 snake_case（28 个文件重命名）
- C# 类转换为主构造函数（8 个类）
- 空 catch 添加异常类型（2 处）
- 新建 GlobalUsings.cs（Health.Infrastructure、Health.WebApi）
- Flutter 移除 go_router，改用 Riverpod 路由栈
- Flutter 移除 flutter_secure_storage，改用 sqflite 持久化
- 修复 Flutter 构建路径（Flutter SDK 迁至 D 盘）
- 后端端口改为 0.0.0.0:5000，支持局域网访问

backend/src/Health.Domain/Entities/medication.cs

@@ -0,0 +1,41 @@
+using Health.Domain.Enums;
+
+namespace Health.Domain.Entities;
+
+/// <summary>
+/// 用药计划
+/// </summary>
+public sealed class Medication
+{
+    public Guid Id { get; set; }
+    public Guid UserId { get; set; }
+    public string Name { get; set; } = string.Empty;
+    public string? Dosage { get; set; }
+    public MedicationFrequency Frequency { get; set; }
+    public List<TimeOnly> TimeOfDay { get; set; } = []; // PostgreSQL TIME[] 数组
+    public DateOnly? StartDate { get; set; }
+    public DateOnly? EndDate { get; set; }
+    public bool IsActive { get; set; } = true;
+    public MedicationSource Source { get; set; }
+    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+    public DateTime UpdatedAt { get; set; } = DateTime.UtcNow;
+
+    public User User { get; set; } = null!;
+    public ICollection<MedicationLog> Logs { get; set; } = [];
+}
+
+/// <summary>
+/// 用药打卡记录
+/// </summary>
+public sealed class MedicationLog
+{
+    public Guid Id { get; set; }
+    public Guid MedicationId { get; set; }
+    public Guid UserId { get; set; }
+    public MedicationLogStatus Status { get; set; }
+    public TimeOnly ScheduledTime { get; set; }
+    public DateTime? ConfirmedAt { get; set; }
+    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+
+    public Medication Medication { get; set; } = null!;
+}