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/components/CustomArticleTab.vue

@@ -116,7 +116,7 @@ const deleteMutation = useMutation({
 const columns = computed<TableColumnsType<ArticleListItem>>(() => [
   { title: t("custom.article.titleColumn"), dataIndex: "title", key: "title", width: 340 },
   { title: t("custom.filters.promptRule"), dataIndex: "prompt_rule_name", key: "prompt_rule_name", width: 160 },
-  { title: t("custom.schedule.platform"), dataIndex: "platforms", key: "platforms", width: 180 },
+  { title: t("custom.schedule.autoPublishPlatforms"), dataIndex: "auto_publish_platforms", key: "auto_publish_platforms", width: 180 },
   { title: t("common.generateStatus"), dataIndex: "generate_status", key: "generate_status", width: 128 },
   { title: t("common.publishStatus"), dataIndex: "publish_status", key: "publish_status", width: 128 },
   { title: t("common.wordCount"), dataIndex: "word_count", key: "word_count", width: 100 },
@@ -319,8 +319,8 @@ onBeforeUnmount(() => {
         <template v-else-if="column.key === 'prompt_rule_name'">
           {{ record.prompt_rule_name || "--" }}
         </template>
-        <template v-else-if="column.key === 'platforms'">
-          {{ formatPublishPlatformList(record.platforms) }}
+        <template v-else-if="column.key === 'auto_publish_platforms'">
+          {{ formatPublishPlatformList(record.auto_publish_platforms) }}
         </template>
         <template v-else-if="column.key === 'generate_status'">
           <ArticleGenerateStatus :status="record.generate_status" />