fix: replace 'error' with 'exc' in error_handler middleware

Changed logger.error keyword argument from 'error' to 'exc' to avoid
Logger._log() errors in the error handler middleware.

aitbc/middleware/error_handler.py

@@ -43,7 +43,7 @@ class ErrorHandlerMiddleware(BaseHTTPMiddleware):
         except Exception as e:
             logger.error(
                 "Unhandled exception",
-                error=str(e),
+                exc=str(e),
                 path=request.url.path,
                 method=request.method,
                 exc_info=True,