feat: 文件存储安全加固 + 认证增强 + 媒体URL保护 + provider 重构

## 后端安全加固
- 新增 UserUploadPathResolver: 用户上传文件路径安全解析, 防目录穿越
- LocalReportFileStorage: 文件存储路径安全加固
- local_account_file_cleanup: 账号删除时文件清理逻辑增强
- AuthService: 认证逻辑增强
- file_endpoints / report_endpoints: 文件访问接口安全加固
- ai_chat_endpoints / doctor_endpoints: 接口安全调整
- Program.cs: 服务注册调整

## 前端认证与媒体
- 新增 authenticated_network_image.dart: 带认证的图片加载组件
- auth_provider: 认证状态管理大幅增强(+173)
- api_client: 网络客户端增强(+124)
- chat_provider: 聊天 provider 重构(+76)
- omron_device_provider: 蓝牙设备 provider 增强(+53)
- sse_handler: SSE 处理增强(+35)
- consultation_provider / data_providers / conversation_history_provider: 调整

## 页面调整
- remaining_pages: 健康档案/饮食记录等页面增强(+115)
- home_page / chat_messages_view: 主页微调
- doctor 端多页微调(consultations/dashboard/followups/patient_detail/profile/report_detail/reports)
- report_pages / settings_pages / notification_prefs_page: 微调
- device_scan_page / diet_capture_page / admin_home_page: 微调

## 测试
- 新增 file_path_security_tests: 文件路径安全测试
- 新增 protected_media_url_test: 媒体URL保护测试
- 新增 user_session_identity_test: 用户会话身份测试
- account_deletion_tests / application_service_tests / auth_tests: 更新

backend/src/Health.Application/AI/AttachmentContextContracts.cs

@@ -16,5 +16,5 @@ public interface IAttachmentContextBuilder
     /// <summary>
     /// 根据 imageUrl 或 pdfUrl 构建附件上下文。两个都为空返回 null。
     /// </summary>
-    Task<AttachmentContext?> BuildAsync(string? imageUrl, string? pdfUrl, CancellationToken ct);
+    Task<AttachmentContext?> BuildAsync(Guid userId, string? imageUrl, string? pdfUrl, CancellationToken ct);
 }

backend/src/Health.Application/Calendars/CalendarService.cs

@@ -40,7 +40,7 @@ public sealed class CalendarService(ICalendarRepository calendar) : ICalendarSer
             .Select(i => new { type = i.ExerciseType, duration = i.DurationMinutes, isCompleted = i.IsCompleted, scheduledDate = i.ScheduledDate })
             .ToList();
         var followUps = snapshot.FollowUps
-            .Where(f => DateOnly.FromDateTime(f.ScheduledAt) == date)
+            .Where(f => BeijingDate(f.ScheduledAt) == date)
             .Select(f => new { f.Title, f.DoctorName, f.Department, status = f.Status.ToString() })
             .ToList();
 
@@ -67,7 +67,7 @@ public sealed class CalendarService(ICalendarRepository calendar) : ICalendarSer
                 entries.Add(new CalendarEntry("exercise", new { type = "exercise", name = item.ExerciseType, duration = item.DurationMinutes, isCompleted = item.IsCompleted, scheduledDate = item.ScheduledDate }));
         }
 
-        foreach (var followUp in snapshot.FollowUps.Where(f => DateOnly.FromDateTime(f.ScheduledAt) == date))
+        foreach (var followUp in snapshot.FollowUps.Where(f => BeijingDate(f.ScheduledAt) == date))
         {
             entries.Add(new CalendarEntry("followup", new
             {
@@ -88,5 +88,14 @@ public sealed class CalendarService(ICalendarRepository calendar) : ICalendarSer
         && (medication.StartDate == null || medication.StartDate <= date)
         && (medication.EndDate == null || medication.EndDate >= date);
 
+    private static DateOnly BeijingDate(DateTime value)
+    {
+        // EF 从 timestamptz 读取的是 UTC；单元测试及旧内存对象可能是 Unspecified。
+        var beijing = value.Kind == DateTimeKind.Unspecified
+            ? value
+            : value.ToUniversalTime().AddHours(8);
+        return DateOnly.FromDateTime(beijing);
+    }
+
     private sealed record CalendarEntry(string Type, object Value);
 }

backend/src/Health.Application/Reports/ReportService.cs

@@ -94,7 +94,7 @@ public sealed class ReportService(
     public static ReportDto ToDto(Report report) => new(
         report.Id,
         report.UserId,
-        report.FileUrl,
+        $"/api/reports/{report.Id}/file",
         report.FileType.ToString(),
         report.Category.ToString(),
         report.Status.ToString(),