fix: 修复文件下载时文件名乱码问题

- 上传时设置 Content-Disposition 头保存原始文件名
- 支持中文文件名的 URL 编码

backend/src/main/java/com/designhub/service/S3Service.java

@@ -89,11 +89,20 @@ public class S3Service {
             // 创建S3客户端
             S3Client s3Client = createS3Client(config);
             
+            // 对原始文件名进行URL编码，用于Content-Disposition头
+            String encodedFilename;
+            try {
+                encodedFilename = java.net.URLEncoder.encode(originalFilename, "UTF-8").replace("+", "%20");
+            } catch (Exception e) {
+                encodedFilename = originalFilename;
+            }
+            String contentDisposition = "attachment; filename*=UTF-8''" + encodedFilename;
+            
             // 根据文件大小选择上传方式
             if (file.getSize() > MULTIPART_THRESHOLD) {
                 // 大文件使用分块上传
                 log.info("文件大小 {} bytes，使用分块上传: {}", file.getSize(), originalFilename);
-                uploadMultipart(s3Client, config, file, filePath);
+                uploadMultipart(s3Client, config, file, filePath, contentDisposition);
             } else {
                 // 小文件使用普通上传
                 log.info("文件大小 {} bytes，使用普通上传: {}", file.getSize(), originalFilename);
@@ -101,6 +110,7 @@ public class S3Service {
                         .bucket(config.getBucket())
                         .key(filePath)
                         .contentType(file.getContentType())
+                        .contentDisposition(contentDisposition)
                         .build();
                 s3Client.putObject(putObjectRequest, RequestBody.fromInputStream(file.getInputStream(), file.getSize()));
             }
@@ -134,7 +144,7 @@ public class S3Service {
     /**
      * 分块上传大文件
      */
-    private void uploadMultipart(S3Client s3Client, S3Config config, MultipartFile file, String filePath) throws IOException {
+    private void uploadMultipart(S3Client s3Client, S3Config config, MultipartFile file, String filePath, String contentDisposition) throws IOException {
         String uploadId = null;
         
         try {
@@ -143,6 +153,7 @@ public class S3Service {
                     .bucket(config.getBucket())
                     .key(filePath)
                     .contentType(file.getContentType())
+                    .contentDisposition(contentDisposition)
                     .build();
             
             CreateMultipartUploadResponse createResponse = s3Client.createMultipartUpload(createRequest);