修改学生加入练习提示词

src/views/targetImprove/practice/knowledgeGraph.vue

@@ -648,8 +648,7 @@ export default {
           this.$message.success('已加入练习成功');
           this.$set(this.addedKnowledgeIds, String(knowledgeId), true);
         } else {
-          const msg = (res && res.message) || '加入练习失败';
-          this.$message.error(msg);
+          this.$message.error(res.msg);
         }
       }).catch(err => {
         console.error('[KnowledgeGraph] addExercise 接口异常:', err);