feat(publish): unify image fetch failure message across adapters

Consolidate per-platform cover/image fetch failure prompts into a single
PUBLISH_IMAGE_FETCH_FAILED_MESSAGE constant shared by baijiahao, bilibili,
dongchedi, qiehao, smzdm, and zol adapters, and generalize the normalizer
to match any *_image_fetch_failed / *_cover_fetch_failed code. Also split
desktop publish list loading into initial vs manual-refresh states so the
refresh button no longer blanks the table, and fix admin-web active-task
detection to cover all pending statuses.

apps/desktop-client/src/main/adapters/baijiahao.ts

@@ -7,6 +7,7 @@ import {
   prepareBaijiahaoMarkdown,
 } from '../../../../../packages/publisher-platforms/src/baijiahao'
 
+import { PUBLISH_IMAGE_FETCH_FAILED_MESSAGE } from '../../shared/publisher-errors'
 import { resolveDesktopApiURL } from '../transport/api-client'
 import type { PublishAdapter, PublishAdapterContext } from './base'
 import {
@@ -436,7 +437,7 @@ function failureResult(
   ) {
     return {
       status: 'failed',
-      summary: '百家号封面文件读取失败，请重新上传封面图后重试。',
+      summary: PUBLISH_IMAGE_FETCH_FAILED_MESSAGE,
       error: {
         code: 'baijiahao_cover_fetch_failed',
         message,