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.WebApi/BackgroundServices/medication_reminder_service.cs

@@ -0,0 +1,61 @@
+namespace Health.WebApi.BackgroundServices;
+
+/// <summary>
+/// 用药提醒定时扫描服务（每分钟检查一次）
+/// </summary>
+public sealed class MedicationReminderService(IServiceScopeFactory scopeFactory, ILogger<MedicationReminderService> logger) : BackgroundService
+{
+    private readonly IServiceScopeFactory _scopeFactory = scopeFactory;
+    private readonly ILogger<MedicationReminderService> _logger = logger;
+
+    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+    {
+        _logger.LogInformation("用药提醒服务已启动");
+
+        while (!stoppingToken.IsCancellationRequested)
+        {
+            try
+            {
+                await ProcessReminders(stoppingToken);
+            }
+            catch (Exception ex)
+            {
+                _logger.LogError(ex, "用药提醒扫描异常");
+            }
+
+            await Task.Delay(TimeSpan.FromMinutes(1), stoppingToken);
+        }
+    }
+
+    private async Task ProcessReminders(CancellationToken ct)
+    {
+        using var scope = _scopeFactory.CreateScope();
+        var db = scope.ServiceProvider.GetRequiredService<AppDbContext>();
+        // 使用北京时间（UTC+8）
+        var beijingNow = DateTime.UtcNow.AddHours(8);
+        var beijingTime = TimeOnly.FromDateTime(beijingNow);
+        var today = DateOnly.FromDateTime(beijingNow);
+
+        // 查询：启用的用药计划 AND 服药时间在当前时间前后5分钟窗口内（防止服务重启错过提醒）
+        var windowStart = beijingTime.AddMinutes(-5);
+        var medications = await db.Medications
+            .Where(m => m.IsActive)
+            .Where(m => m.TimeOfDay.Any(t => t >= windowStart && t <= beijingTime))
+            .ToListAsync(ct);
+
+        foreach (var med in medications)
+        {
+            // 检查今天是否已打卡
+            var alreadyLogged = await db.MedicationLogs
+                .AnyAsync(l => l.MedicationId == med.Id
+                    && l.CreatedAt.Date == beijingNow.Date
+                    && l.Status == MedicationLogStatus.Taken, ct);
+
+            if (alreadyLogged) continue;
+
+            // TODO: 调用极光推送发送用药提醒
+            _logger.LogInformation("用药提醒: 用户 {UserId} 药品 {Name} {Dosage} 时间 {Time}",
+                med.UserId, med.Name, med.Dosage, beijingTime);
+        }
+    }
+}