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/views/TemplatesView.vue

@@ -161,7 +161,7 @@ const recentTemplateArticles = computed<ArticleListItem[]>(() =>
       prompt_rule_id: null,
       prompt_rule_name: null,
       generation_mode: article.generation_mode,
-      platforms: [],
+      auto_publish_platforms: [],
       generate_status: article.generate_status,
       publish_status: article.publish_status,
       title: article.title,