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/InstantTaskTab.vue

@@ -80,7 +80,7 @@ const columns = computed<TableColumnsType<InstantTaskItem>>(() => [
   { title: t("custom.schedule.rule"), dataIndex: "prompt_rule_name", key: "prompt_rule_name", width: 180 },
   { title: t("custom.instant.executionStatus"), dataIndex: "status", key: "status", width: 140 },
   { title: t("custom.instant.executionTime"), dataIndex: "execution_time", key: "execution_time", width: 170 },
-  { title: t("custom.schedule.platform"), dataIndex: "platforms", key: "platforms", width: 220 },
+  { title: t("custom.schedule.autoPublishPlatforms"), dataIndex: "auto_publish_platforms", key: "auto_publish_platforms", width: 220 },
   { title: t("custom.task.generateCount"), dataIndex: "generate_count", key: "generate_count", width: 120 },
   { title: t("custom.instant.createdTime"), dataIndex: "created_at", key: "created_at", width: 170 },
   { title: t("common.actions"), key: "actions", width: 88, fixed: "right", align: "right" },
@@ -235,8 +235,8 @@ onBeforeUnmount(() => {
         <template v-else-if="column.key === 'execution_time'">
           {{ formatDateTime(record.execution_time) }}
         </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_count'">
           {{ record.generate_count || 1 }}