课程库 Excel 导入导出已完成：

支持下载标准导入模板。
导出严格沿用当前关键词、学院、分类、课程性质和状态筛选。
以课程编码为唯一键：存在则更新，不存在则新增。
校验学院编码、课程分类、课程性质、学分学时及考核方式。
整批原子导入，任一行错误则全部不写入，并提示具体行号。
学院管理员仍只能维护本学院的专业课和实践课，无法借 Excel 越权。
界面入口沿用现有课程库工具栏样式。

src/Jiaowu.Api/Controllers/CoursesController.cs

@@ -28,6 +28,7 @@ public sealed class CoursesController(
         int pageSize = 20,
         string? keyword = null,
         Guid? collegeId = null,
+        Guid? categoryId = null,
         CourseNature? nature = null,
         bool? isEnabled = null,
         CancellationToken cancellationToken = default)
@@ -42,6 +43,8 @@ public sealed class CoursesController(
         var source = ScopedCourses().AsNoTracking();
         if (collegeId.HasValue)
             source = source.Where(x => x.CollegeId == collegeId.Value);
+        if (categoryId.HasValue)
+            source = source.Where(x => x.CourseCategoryId == categoryId.Value);
         if (nature.HasValue)
             source = source.Where(x => x.Nature == nature.Value);
         if (isEnabled.HasValue)
@@ -69,6 +72,9 @@ public sealed class CoursesController(
                 x.EnglishName,
                 x.CollegeId,
                 CollegeName = x.College!.Name,
+                x.CourseCategoryId,
+                CategoryCode = x.CourseCategory != null ? x.CourseCategory.Code : null,
+                CategoryName = x.CourseCategory != null ? x.CourseCategory.Name : null,
                 x.Credits,
                 x.TotalHours,
                 x.LectureHours,
@@ -106,6 +112,7 @@ public sealed class CoursesController(
             Name = request.Name.Trim(),
             EnglishName = Normalize(request.EnglishName),
             CollegeId = request.CollegeId,
+            CourseCategoryId = request.CourseCategoryId,
             Credits = request.Credits,
             TotalHours = request.TotalHours,
             LectureHours = request.LectureHours,
@@ -137,6 +144,7 @@ public sealed class CoursesController(
         entity.Name = request.Name.Trim();
         entity.EnglishName = Normalize(request.EnglishName);
         entity.CollegeId = request.CollegeId;
+        entity.CourseCategoryId = request.CourseCategoryId;
         entity.Credits = request.Credits;
         entity.TotalHours = request.TotalHours;
         entity.LectureHours = request.LectureHours;
@@ -167,6 +175,10 @@ public sealed class CoursesController(
         if (!CanManage(request.CollegeId, request.Nature)) return Forbid();
         if (!await db.Colleges.AnyAsync(x => x.Id == request.CollegeId, cancellationToken))
             return ValidationProblem("所选学院不存在。");
+        if (!await db.CourseCategories.AnyAsync(
+                x => x.Id == request.CourseCategoryId && x.IsEnabled,
+                cancellationToken))
+            return ValidationProblem("所选课程分类不存在或已停用。");
         if (request.LectureHours + request.PracticeHours > request.TotalHours)
             return ValidationProblem("讲授学时与实践学时之和不能超过总学时。");
         return null;
@@ -242,6 +254,7 @@ public sealed record CourseRequest(
     [Required, MaxLength(100)] string Name,
     [MaxLength(150)] string? EnglishName,
     Guid CollegeId,
+    Guid CourseCategoryId,
     [Range(typeof(decimal), "0.1", "99")] decimal Credits,
     [Range(1, 1000)] int TotalHours,
     [Range(0, 1000)] int LectureHours,