优化学业预警检测：

通知阶段移除逐条查询学生、规则、辅导员的 N+1 数据库访问。
不及格预警从“每个学生一次统计 + 一次查重”改为批量分组统计与一次性已有记录集合查询。
保持原有阈值、去重、通知内容与权限行为。

src/Jiaowu.Api/Controllers/WarningsController.cs

@@ -101,17 +101,23 @@ public sealed class WarningsController(AppDbContext db, ICurrentUserDataScope sc
             db.WarningRecords.AddRange(generated);
             await db.SaveChangesAsync(ct);
 
+            var studentsById = studentInfos.ToDictionary(student => student.Id);
+            var rulesByType = rules.ToDictionary(rule => rule.Type);
+            var classIds = studentInfos.Select(student => student.ClassId).Distinct().ToArray();
+            var counselorsByClass = await db.AdministrativeClasses.AsNoTracking()
+                .WhereIn(classIds, item => item.Id)
+                .Where(item => item.CounselorUserId != null)
+                .Select(item => new { item.Id, CounselorUserId = item.CounselorUserId!.Value })
+                .ToDictionaryAsync(item => item.Id, item => item.CounselorUserId, ct);
             foreach (var w in generated)
             {
-                var si = studentInfos.First(s => s.Id == w.StudentId);
-                var r = rules.First(r => r.Type == w.Type);
+                var si = studentsById[w.StudentId];
+                var r = rulesByType[w.Type];
                 if (r.NotifyStudent && si.UserId.HasValue)
                     await NotificationService.SendAsync(db, si.UserId.Value, "学业预警", w.Detail, "/warnings", ct, NotificationCategory.Warning);
-                if (r.NotifyCounselor)
+                if (r.NotifyCounselor && counselorsByClass.TryGetValue(si.ClassId, out var counselorId))
                 {
-                    var counselorId = await db.AdministrativeClasses.Where(c => c.Id == si.ClassId && c.CounselorUserId != null).Select(c => c.CounselorUserId!.Value).FirstOrDefaultAsync(ct);
-                    if (counselorId != default)
-                        await NotificationService.SendAsync(db, counselorId, "学生学业预警", $"{si.Name}：{w.Detail}", "/warnings", ct, NotificationCategory.Warning);
+                    await NotificationService.SendAsync(db, counselorId, "学生学业预警", $"{si.Name}：{w.Detail}", "/warnings", ct, NotificationCategory.Warning);
                 }
             }
         }
@@ -197,17 +203,31 @@ public sealed class WarningsController(AppDbContext db, ICurrentUserDataScope sc
     // ═══════════ Detection logic ═══════════
     private async Task<List<WarningRecord>> DetectFailedCredits(WarningRule rule, Guid termId, List<StudentInfo> students, CancellationToken ct)
     {
-        var records = new List<WarningRecord>();
-        foreach (var s in students)
-        {
-            var failed = await db.GradeRecords.CountAsync(x => x.StudentId == s.Id && x.GradeSheet!.TeachingTask!.AcademicTermId == termId && x.GradeSheet.Status == GradeSheetStatus.Published && x.TotalScore < 60, ct);
-            if (failed >= rule.Threshold)
+        var studentIds = students.Select(student => student.Id).ToArray();
+        var existingStudentIds = await db.WarningRecords.AsNoTracking()
+            .Where(record => record.AcademicTermId == termId && record.Type == rule.Type)
+            .Select(record => record.StudentId)
+            .ToHashSetAsync(ct);
+        var failedByStudent = await db.GradeRecords.AsNoTracking()
+            .Where(record => studentIds.Contains(record.StudentId) &&
+                             record.GradeSheet!.TeachingTask!.AcademicTermId == termId &&
+                             record.GradeSheet.Status == GradeSheetStatus.Published &&
+                             record.TotalScore < 60)
+            .GroupBy(record => record.StudentId)
+            .Select(group => new { StudentId = group.Key, Failed = group.Count() })
+            .ToListAsync(ct);
+        return failedByStudent
+            .Where(item => item.Failed >= rule.Threshold &&
+                           !existingStudentIds.Contains(item.StudentId))
+            .Select(item => new WarningRecord
             {
-                if (await db.WarningRecords.AnyAsync(x => x.StudentId == s.Id && x.AcademicTermId == termId && x.Type == WarningType.FailedCredits, ct)) continue;
-                records.Add(new WarningRecord { StudentId = s.Id, Type = rule.Type, TriggerValue = failed, Detail = $"不及格课程 {failed} 门，达到预警阈值 {rule.Threshold} 门。", AcademicTermId = termId });
-            }
-        }
-        return records;
+                StudentId = item.StudentId,
+                Type = rule.Type,
+                TriggerValue = item.Failed,
+                Detail = $"不及格课程 {item.Failed} 门，达到预警阈值 {rule.Threshold} 门。",
+                AcademicTermId = termId
+            })
+            .ToList();
     }
 
     private async Task<List<WarningRecord>> DetectLowGPA(WarningRule rule, Guid termId, List<StudentInfo> students, CancellationToken ct)