点名、成绩册统一读取“行政班在籍学生 ∪ 已选课学生”，不再错误显示 0 人。

教师选课名单改为展示全部本人教学班及完整学生名单，支持 Excel 导出。
调停课改用教师专用教学班接口，并在服务端限制只能操作本人教学班。

src/Jiaowu.Api/Controllers/GradesController.cs

@@ -6,6 +6,7 @@ using Jiaowu.Api.Infrastructure.Auth;
 using Jiaowu.Api.Infrastructure.Excel;
 using Jiaowu.Api.Infrastructure.Grades;
 using Jiaowu.Api.Infrastructure.Persistence;
+using Jiaowu.Api.Infrastructure.Teaching;
 using Microsoft.AspNetCore.Authorization;
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.EntityFrameworkCore;
@@ -134,15 +135,13 @@ public sealed class GradesController(
                 cancellationToken))
             return ConflictProblem("该教学班已经建立成绩单。");
 
-        var studentIds = await db.CourseEnrollments.AsNoTracking()
-            .Where(x =>
-                x.Status == CourseEnrollmentStatus.Enrolled &&
-                x.CourseSelectionOffering!.TeachingTaskId == task.Id)
-            .Select(x => x.StudentId)
-            .Distinct()
+        var studentIds = await TeachingTaskRosterQuery
+            .ForTask(db, task.Id)
+            .AsNoTracking()
+            .Select(x => x.Id)
             .ToListAsync(cancellationToken);
         if (studentIds.Count == 0)
-            return ConflictProblem("教学班当前没有有效选课学生，无法建立成绩单。");
+            return ConflictProblem("教学班当前没有有效学生，无法建立成绩单。");
 
         var sheet = new GradeSheet
         {