Fix: 修复文件上传临时文件丢失问题

问题：
- Docker 环境下上传文件时出现 FileNotFoundException
- Tomcat 在异步任务执行前清理了临时文件 /tmp/tomcat.xxx/work/...

解决方案：
1. 配置 multipart.location 为持久化目录 ./data/upload-temp
2. 设置 file-size-threshold: 0 强制立即写入磁盘
3. 修改 SftpController.upload() 方法：
   - 在异步任务执行前将 MultipartFile 保存到持久化位置
   - 异步任务从保存的文件读取而非 MultipartFile.getInputStream()
   - 上传完成或失败后自动清理临时文件

影响范围：
- backend/src/main/resources/application.yml
- backend/src/main/java/com/sshmanager/controller/SftpController.java

backend/src/main/java/com/sshmanager/controller/SftpController.java

@@ -290,11 +290,21 @@ public class SftpController {
             @RequestParam String path,
             @RequestParam("file") MultipartFile file,
             Authentication authentication) {
+        java.io.File tempFile = null;
         try {
             Long userId = getCurrentUserId(authentication);
             String taskId = UUID.randomUUID().toString();
             String taskKey = uploadTaskKey(userId, taskId);
             
+            // Save file to persistent location before async processing
+            java.io.File uploadTempDir = new java.io.File("./data/upload-temp");
+            if (!uploadTempDir.exists()) {
+                uploadTempDir.mkdirs();
+            }
+            tempFile = new java.io.File(uploadTempDir, taskId + "_" + file.getOriginalFilename());
+            file.transferTo(tempFile);
+            final java.io.File savedFile = tempFile;
+            
             UploadTaskStatus status = new UploadTaskStatus(taskId, userId, connectionId, 
                 path, file.getOriginalFilename(), file.getSize());
             status.setController(this);
@@ -308,11 +318,11 @@ public class SftpController {
                         try {
                             SftpService.SftpSession session = getOrCreateSession(connectionId, userId);
                             String remotePath = (path == null || path.isEmpty() || path.equals("/"))
-                                ? "/" + file.getOriginalFilename()
+                                ? "/" + savedFile.getName().substring(savedFile.getName().indexOf("_") + 1)
-                                : (path.endsWith("/") ? path + file.getOriginalFilename() : path + "/" + file.getOriginalFilename());
+                                : (path.endsWith("/") ? path + savedFile.getName().substring(savedFile.getName().indexOf("_") + 1) : path + "/" + savedFile.getName().substring(savedFile.getName().indexOf("_") + 1));
                             
                             AtomicLong transferred = new AtomicLong(0);
-                            try (java.io.InputStream in = file.getInputStream()) {
+                            try (java.io.InputStream in = new java.io.FileInputStream(savedFile)) {
                                 sftpService.upload(session, remotePath, in, new SftpService.TransferProgressListener() {
                                     @Override
                                     public void onStart(long totalBytes) {
@@ -334,10 +344,19 @@ public class SftpController {
                                 existing.disconnect();
                             }
                             throw new RuntimeException(e);
+                        } finally {
+                            // Clean up temp file after upload completes
+                            if (savedFile.exists()) {
+                                savedFile.delete();
+                            }
                         }
                     });
                 } catch (Exception e) {
                     status.markError(e.getMessage() != null ? e.getMessage() : "Upload failed");
+                    // Clean up temp file on error
+                    if (savedFile.exists()) {
+                        savedFile.delete();
+                    }
                 }
             });
             status.setFuture(future);
@@ -347,6 +366,10 @@ public class SftpController {
             result.put("message", "Upload started");
             return ResponseEntity.ok(result);
         } catch (Exception e) {
+            // Clean up temp file if initial save failed
+            if (tempFile != null && tempFile.exists()) {
+                tempFile.delete();
+            }
             Map<String, Object> error = new HashMap<>();
             error.put("error", e.getMessage());
             return ResponseEntity.status(500).body(error);

backend/src/main/resources/application.yml

@@ -9,6 +9,8 @@ spring:
     multipart:
       max-file-size: 2048MB
       max-request-size: 2048MB
+      location: ./data/upload-temp
+      file-size-threshold: 0
   datasource:
     url: jdbc:h2:file:./data/sshmanager;DB_CLOSE_DELAY=-1
     driver-class-name: org.h2.Driver