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/Infrastructure/Persistence/AppDbContext.cs

@@ -19,6 +19,7 @@ public sealed class AppDbContext(DbContextOptions<AppDbContext> options)
     public DbSet<AcademicTerm> AcademicTerms => Set<AcademicTerm>();
     public DbSet<Teacher> Teachers => Set<Teacher>();
     public DbSet<Student> Students => Set<Student>();
+    public DbSet<CourseCategory> CourseCategories => Set<CourseCategory>();
     public DbSet<Course> Courses => Set<Course>();
     public DbSet<CurriculumPlan> CurriculumPlans => Set<CurriculumPlan>();
     public DbSet<CurriculumModule> CurriculumModules => Set<CurriculumModule>();
@@ -78,6 +79,7 @@ public sealed class AppDbContext(DbContextOptions<AppDbContext> options)
         ConfigureCatalog<Building>(builder);
         ConfigureCatalog<Classroom>(builder);
         ConfigureCatalog<AcademicTerm>(builder);
+        ConfigureCatalog<CourseCategory>(builder);
         ConfigureCatalog<Course>(builder);
 
         builder.Entity<College>()
@@ -167,10 +169,15 @@ public sealed class AppDbContext(DbContextOptions<AppDbContext> options)
             entity.Property(x => x.Credits).HasPrecision(5, 2);
             entity.Property(x => x.Description).HasMaxLength(1000);
             entity.HasIndex(x => new { x.CollegeId, x.Nature });
+            entity.HasIndex(x => x.CourseCategoryId);
             entity.HasOne(x => x.College)
                 .WithMany()
                 .HasForeignKey(x => x.CollegeId)
                 .OnDelete(DeleteBehavior.Restrict);
+            entity.HasOne(x => x.CourseCategory)
+                .WithMany()
+                .HasForeignKey(x => x.CourseCategoryId)
+                .OnDelete(DeleteBehavior.Restrict);
         });
 
         builder.Entity<CurriculumPlan>(entity =>