feat: 将工作流与 FAQ 上传上限扩至 20MB

- 同步管理端、用户中心与后端工作流文件校验

- 扩展 FAQ 普通及分享上传限制并补充边界测试

easyflow-ui-usercenter/app/src/views/ai/workflow/components/workflowFileValue.ts

@@ -21,7 +21,7 @@ export interface WorkflowResourceLike {
 
 export const WORKFLOW_FILE_LIMITS = {
   maxCount: 10,
-  maxSingleSize: 5 * 1024 * 1024,
+  maxSingleSize: 20 * 1024 * 1024,
   maxTotalSize: 50 * 1024 * 1024,
 } as const;