Standardize async offloading behind shared executor helper

backend/app/services/config_service.py

@@ -13,6 +13,7 @@ routers can serialise them directly.
 from __future__ import annotations
 
 import asyncio
+from app.utils.async_utils import run_blocking
 import contextlib
 import re
 from pathlib import Path
@@ -750,8 +751,8 @@ async def read_fail2ban_log(
     loop = asyncio.get_event_loop()
 
     total_lines, raw_lines = await asyncio.gather(
-        loop.run_in_executor(None, _count_file_lines, resolved_str),
-        loop.run_in_executor(None, _read_tail_lines, resolved_str, lines),
+        run_blocking( _count_file_lines, resolved_str),
+        run_blocking( _read_tail_lines, resolved_str, lines),
     )
 
     filtered = (