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/consultation.cs

@@ -0,0 +1,53 @@
+using Health.Domain.Enums;
+
+namespace Health.Domain.Entities;
+
+/// <summary>
+/// 问诊会话
+/// </summary>
+public sealed class Consultation
+{
+    public Guid Id { get; set; }
+    public Guid UserId { get; set; }
+    public Guid DoctorId { get; set; }
+    public ConsultationStatus Status { get; set; }
+    public int Month { get; set; }               // 所属月份，用于配额计算
+    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+    public DateTime? ClosedAt { get; set; }
+
+    public User User { get; set; } = null!;
+    public Doctor Doctor { get; set; } = null!;
+    public ICollection<ConsultationMessage> Messages { get; set; } = [];
+}
+
+/// <summary>
+/// 问诊消息
+/// </summary>
+public sealed class ConsultationMessage
+{
+    public Guid Id { get; set; }
+    public Guid ConsultationId { get; set; }
+    public ConsultationSenderType SenderType { get; set; }
+    public string? SenderName { get; set; }
+    public string Content { get; set; } = string.Empty;
+    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+
+    public Consultation Consultation { get; set; } = null!;
+}
+
+/// <summary>
+/// 医生
+/// </summary>
+public sealed class Doctor
+{
+    public Guid Id { get; set; }
+    public string Name { get; set; } = string.Empty;
+    public string? Title { get; set; }           // 主任医师/副主任医师
+    public string? Department { get; set; }      // 心血管内科/营养科
+    public string? AvatarUrl { get; set; }
+    public string? Introduction { get; set; }
+    public bool IsActive { get; set; } = true;
+    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+
+    public ICollection<Consultation> Consultations { get; set; } = [];
+}