fix: 定时任务 cron 表达式改为从配置读取，消除硬编码

app/scheduler/jobs.py

@@ -1,6 +1,7 @@
 import logging
 
 from apscheduler.schedulers.asyncio import AsyncIOScheduler
+from apscheduler.triggers.cron import CronTrigger
 
 from app.api.deps import get_crawl_service
 from app.config import settings
@@ -29,17 +30,15 @@ async def scheduled_crawl():
 def start_scheduler():
     if not settings.scheduler_enabled:
         return
+    trigger = CronTrigger.from_crontab(settings.scheduler_cron, timezone="Asia/Shanghai")
     scheduler.add_job(
         scheduled_crawl,
-        "cron",
-        hour="8,14,18",
-        minute="0",
+        trigger=trigger,
         id="scheduled_crawl",
         name="定时爬取",
-        timezone="Asia/Shanghai",
     )
     scheduler.start()
-    logger.info("APScheduler 已启动 (8:00, 14:00, 18:00)")
+    logger.info(f"APScheduler 已启动 (cron: {settings.scheduler_cron})")
 
 
 def shutdown_scheduler():