feat(article): expose auto_publish_platforms derived from publish accounts

Replace the freeform `platforms` field on articles/tasks (parsed out of
wizard_state/input_params JSON) with `auto_publish_platforms`, resolved
by joining schedule publish accounts to platform_accounts. The migration
strips the legacy keys from existing rows so the new field is the single
source of truth.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/admin-web/src/i18n/messages/zh-CN.ts

@@ -1300,9 +1300,9 @@ const zhCN = {
       name: "任务名称",
       rule: "关联规则",
       cron: "执行频率",
+      autoPublishPlatforms: "自动发布平台",
       autoPublish: "自动发布",
       manualPublish: "手动发布",
-      autoPublishAccountCount: "自动 · {count} 个账号",
       nextRun: "下次执行",
       startAt: "开始时间",
       endAt: "结束时间",