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-executor.test.mjs

@@ -32,6 +32,10 @@ test('looksLikeScheduledTaskNonDelivery detects clarification replies', () => {
     looksLikeScheduledTaskNonDelivery('页面已生成：https://example.com/news.html'),
     false,
   );
+  assert.equal(
+    looksLikeScheduledTaskNonDelivery('好的', { readyPaths: ['public/news.html'] }),
+    false,
+  );
 });
 
 test('extractScheduledTaskDeliveryText reads last assistant message', () => {