fix: remove f-string prefix without placeholders in miku.py

Fixed F541 linting warning at line 324 where logger.info used
f-string syntax without any placeholders.

Generated with [codeagent](https://github.com/qbox/codeagent)
Co-authored-by: callmefisher <[email protected]>

Author: xgopilot

src/mcp_server/core/miku/miku.py

@@ -321,7 +321,7 @@ async def query_traffic_stats(self, begin: str, end: str, g: str = "5min",
                 text = await response.text()
 
                 if status == 200:
-                    logger.info(f"Successfully retrieved traffic stats")
+                    logger.info("Successfully retrieved traffic stats")
                     return {
                         "status": "success",
                         "begin": begin,