优化体验，新增多项功能，美化界面

backend/src/services/measurementStorage.js

@@ -3,7 +3,7 @@
  * 本地开发环境：使用 AWS_ACCESS_KEY_ID / AWS_SECRET_ACCESS_KEY
  * 正式环境：通过 IAM 角色访问 S3（无需配置密钥）
  */
-const { S3Client, PutObjectCommand } = require('@aws-sdk/client-s3');
+const { S3Client, PutObjectCommand, GetObjectCommand } = require('@aws-sdk/client-s3');
 const logger = require('../config/logger');
 
 const AWS_REGION = process.env.AWS_REGION || 'eu-central-1';
@@ -79,7 +79,36 @@ async function uploadMeasurementToS3(buffer, params) {
   }
 }
 
+/**
+ * 从 S3 读取频响 CSV 文件
+ * @param {object} params - 路径参数（同 buildMeasurementKey）
+ * @returns {Promise<{ key: string, content: string }>}
+ */
+async function getMeasurementFromS3(params) {
+  const key = buildMeasurementKey(params);
+  const client = getS3Client();
+
+  try {
+    const response = await client.send(
+      new GetObjectCommand({
+        Bucket: S3_BUCKET,
+        Key: key,
+      })
+    );
+    const content = await response.Body.transformToString('utf-8');
+    logger.info(`Measurement read from s3://${S3_BUCKET}/${key}`);
+    return { key, content };
+  } catch (e) {
+    if (e.name === 'NoSuchKey' || e.$metadata?.httpStatusCode === 404) {
+      throw new Error('S3 上未找到该型号的频响文件');
+    }
+    logger.error(`S3 measurement read failed: ${e.message}`);
+    throw new Error(`S3 读取失败：${e.message}`);
+  }
+}
+
 module.exports = {
   uploadMeasurementToS3,
+  getMeasurementFromS3,
   buildMeasurementKey,
 };