fix(scheduled-task): enable worker by default and add WeChat preflight

Scheduled automations were saved but never executed because the worker
required an explicit env flag. Follow H5_REMINDER_WORKER_ENABLED when unset,
add WeChat preflight to write tasks deterministically, and surface worker
warnings on create.

Co-authored-by: Cursor <cursoragent@cursor.com>

scheduled-task-worker-config.mjs

@@ -0,0 +1,18 @@
+/**
+ * Scheduled task worker enablement.
+ * Explicit H5_SCHEDULED_TASK_WORKER_ENABLED=1 always wins.
+ * Explicit =0 always disables.
+ * When unset, follow H5_REMINDER_WORKER_ENABLED so production schedule stacks
+ * that already run reminder worker also execute scheduled automations.
+ */
+export function isScheduledTaskWorkerEnabled(env = process.env) {
+  const explicit = String(env.H5_SCHEDULED_TASK_WORKER_ENABLED ?? '').trim();
+  if (explicit === '1') return true;
+  if (explicit === '0') return false;
+  return env.H5_REMINDER_WORKER_ENABLED === '1';
+}
+
+export function scheduledTaskWorkerDisabledMessage(env = process.env) {
+  if (isScheduledTaskWorkerEnabled(env)) return null;
+  return '任务已保存，但当前环境未开启定时自动执行 Worker；到点不会自动跑任务。请联系管理员开启 H5_SCHEDULED_TASK_WORKER_ENABLED=1，或与 H5_REMINDER_WORKER_ENABLED=1 一并启用。';
+}