Address code review: fix E501 consistency in AGENTS.md, fix exception handling in test_security.py

Agent-Logs-Url: https://github.com/christianlouis/dmarq/sessions/9d256101-34b6-4861-a8cf-7f86f32b54d5

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

AGENTS.md

@@ -105,7 +105,7 @@ black --check backend/app
 isort --check-only backend/app
 
 # Flake8 lint
-flake8 backend/app --max-line-length=100 --extend-ignore=E203,W503
+flake8 backend/app --max-line-length=100 --extend-ignore=E203,W503,E501
 ```
 
 If Black or isort report issues, fix them automatically:

backend/app/tests/test_security.py

@@ -149,5 +149,5 @@ class TestXMLParsingSecurity:
             result = DMARCParser.parse_file(xxe_payload, "test.xml")
             org_name = result.get("org_name", "")
             assert "root:" not in org_name and "/bin" not in org_name
-        except (ValueError, Exception):
+        except Exception:
             pass  # Expected – defusedxml blocks DTD processing