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>

schedule-intent.mjs

@@ -29,7 +29,7 @@ function chineseHourToNumber(value) {
   return map[raw] ?? null;
 }
 
-function parseHourMinute(text) {
+export function parseHourMinute(text) {
   const match = text.match(/(?:早上|上午|清晨|每天早上|每天上午)?([0-9]{1,2}|[零一二两三四五六七八九十]{1,3})(?:点|:|：)(半|[0-9]{1,2}分?)?/);
   if (!match) return null;
   const hour = chineseHourToNumber(match[1]);