Fix backend tests by using per-test temp config dir, align router mocks to service modules, fix log tail helper reference, and add JailNotFoundError.name

backend/app/exceptions.py

@@ -6,6 +6,10 @@ from __future__ import annotations
 class JailNotFoundError(Exception):
     """Raised when a requested jail name does not exist."""
 
+    def __init__(self, name: str) -> None:
+        self.name = name
+        super().__init__(f"Jail not found: {name!r}")
+
 
 class JailOperationError(Exception):
     """Raised when a fail2ban jail operation fails."""

backend/app/services/config_service.py

@@ -719,7 +719,7 @@ async def read_fail2ban_log(
 
     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),
+        loop.run_in_executor(None, log_service._read_tail_lines, resolved_str, lines),
     )
 
     filtered = (