fix: auto-fix code issues (cron)

- 修复重复导入/字段
- 修复异常处理
- 修复PEP8格式问题
- 添加类型注解

backend/rate_limiter.py

@@ -120,7 +120,7 @@ class RateLimiter:
         await counter.add_request()
 
         return RateLimitInfo(
-            allowed=True, remaining=remaining - 1, reset_time=reset_time, retry_after=0
+            allowed=True, remaining=remaining - 1, reset_time=reset_time, retry_after=0,
         )
 
     async def get_limit_info(self, key: str) -> RateLimitInfo:
@@ -195,7 +195,7 @@ def rate_limit(requests_per_minute: int = 60, key_func: Callable | None = None)
 
             if not info.allowed:
                 raise RateLimitExceeded(
-                    f"Rate limit exceeded. Try again in {info.retry_after} seconds."
+                    f"Rate limit exceeded. Try again in {info.retry_after} seconds.",
                 )
 
             return await func(*args, **kwargs)
@@ -208,7 +208,7 @@ def rate_limit(requests_per_minute: int = 60, key_func: Callable | None = None)
 
             if not info.allowed:
                 raise RateLimitExceeded(
-                    f"Rate limit exceeded. Try again in {info.retry_after} seconds."
+                    f"Rate limit exceeded. Try again in {info.retry_after} seconds.",
                 )
 
             return func(*args, **kwargs)