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>

.env.example

@@ -183,6 +183,14 @@ H5_PUBLIC_BASE_URL=http://127.0.0.1:5173
 # MEMIND_WECHAT_SCHEDULE_LLM_MODEL_PROVIDER_KEY_ID=
 # MEMIND_WECHAT_SCHEDULE_LLM_MODEL=deepseek-v4-pro
 
+# 日程 / 定时自动任务 Worker（到点扫描 DB 并执行；默认跟随 H5_REMINDER_WORKER_ENABLED）
+# H5_SCHEDULE_ENABLED=1
+# H5_REMINDER_WORKER_ENABLED=1
+# H5_SCHEDULED_TASK_WORKER_ENABLED=1
+# H5_SCHEDULED_TASK_SCAN_INTERVAL_MS=30000
+# H5_SCHEDULED_TASK_MAX_ATTEMPTS=3
+# H5_SCHEDULED_TASK_EXECUTION_TIMEOUT_MS=900000
+
 # H5 Session stream replay
 # 默认 0：session SSE 仍纯透传 goosed；设 1 时 Portal 持久化 session 事件并支持 Last-Event-ID 重连补发。
 # MEMIND_SESSION_STREAM_REPLAY=0