feat(class): 添加班级删除功能

- 在班级列表表格中新增“操作”列，添加删除按钮
- 实现删除班级的接口调用逻辑
- 删除成功后刷新班级列表
- 删除当前选中班级时清空选中状态
- 添加成功和失败的用户提示信息

enlish-service/src/main/resources/mapper/GradeClassDOMapper.xml

@@ -6,12 +6,27 @@
         <result column="class_id" jdbcType="INTEGER" property="classId" />
         <result column="grade_id" jdbcType="INTEGER" property="gradeId" />
     </resultMap>
-    
+
     <select id="selectByClassIds" resultMap="BaseResultMap">
         select * from grade_class where class_id in
         <foreach collection="classIds" item="classId" separator="," open="(" close=")">
             #{classId}
         </foreach>
     </select>
+    <select id="selectByGradeId" resultType="java.lang.Integer">
+        select count(1)
+        from grade_class
+        where grade_id = #{gradeId}
+    </select>
 
+    <insert id="insert">
+        insert into grade_class
+            (class_id, grade_id)
+        values
+            (#{classId}, #{gradeId})
+    </insert>
+
+    <delete id="deleteByClassId">
+        delete from grade_class where class_id = #{classId}
+    </delete>
 </mapper>