perf: 翻译独立后台循环(1 篇/秒)+ Semaphore 1

之前 fetch_one_source 入库后立即调翻译(可能并发触发腾讯 TMT 限速)
改为独立 translation_loop 后台循环:
- 完全不和 RSS 抓取并行
- 1 篇/秒节拍(Semaphore 1 + sleep 1.0)
- 没活时空闲 5 秒再轮询
- pending/failed 都重试

backend/app/workers/__main__.py

@@ -17,7 +17,7 @@ from sqlalchemy import select
 from app.config import settings
 from app.database import AsyncSessionLocal
 from app.models.source import Source
-from app.workers.pipeline import fetch_one_source, run_once
+from app.workers.pipeline import fetch_one_source, run_once, translation_loop
 
 logger = logging.getLogger("news.worker")
 logging.basicConfig(
@@ -89,6 +89,10 @@ async def main() -> None:
     scheduler.start()
     logger.info("scheduler started with %d jobs", len(scheduler.get_jobs()))
 
+    # 独立的翻译后台循环(不和 RSS 抓取并行;1 篇/秒)
+    translation_task = asyncio.create_task(translation_loop(), name="translation_loop")
+    logger.info("translation_loop task scheduled (1 article/sec)")
+
     stop = asyncio.Event()
 
     def _signal_handler():
@@ -104,7 +108,12 @@ async def main() -> None:
             pass
 
     await stop.wait()
-    logger.info("stopping scheduler")
+    logger.info("stopping scheduler and translation loop")
+    translation_task.cancel()
+    try:
+        await translation_task
+    except asyncio.CancelledError:
+        pass
     scheduler.shutdown(wait=False)