功能: 集成 rclone 高级传输特性 + 全 70+ 后端支持

1. 失败自动重试：rclone Pacer 指数退避，默认 10 次底层 HTTP 重试
2. 带宽限制：配置 bandwidth_limit + Settings 运行时可调
3. 上传实时进度：progressReader + LogHub SSE 推送字节级进度/速率
4. 存储空间查询：StorageAbout 可选接口，GetUsage 返回远端真实空间
5. 全 rclone 后端：backend/all 引入 70+ 后端，新增 rclone 存储类型，
   API 驱动的可搜索后端选择器 + 动态配置表单

server/internal/service/backup_execution_service_test.go

@@ -59,7 +59,7 @@ func newExecutionTestServices(t *testing.T) (*BackupExecutionService, *BackupRec
 	if err := os.MkdirAll(tempDir, 0o755); err != nil {
 		t.Fatalf("MkdirAll tempDir returned error: %v", err)
 	}
-	executionService := NewBackupExecutionService(tasks, records, targets, storageRegistry, runnerRegistry, logHub, retentionService, cipher, nil, tempDir, 2)
+	executionService := NewBackupExecutionService(tasks, records, targets, storageRegistry, runnerRegistry, logHub, retentionService, cipher, nil, tempDir, 2, 10, "")
 	recordService := NewBackupRecordService(records, executionService, logHub)
 	return executionService, recordService, tasks, targets, records, sourceDir, storageDir
 }