tests: centralize script path setup in conftest.py

Add a pytest-discovered tests/conftest.py for the last30days scripts path and
remove duplicate per-file sys.path.insert boilerplate from tests.

Normalize affected imports to rely on the shared scripts path and remove the
now-unneeded E402 suppressions.

tests/test_env_cookies.py

@@ -1,14 +1,10 @@
 """Tests for browser cookie extraction integration in env.py."""
 
 import os
-import sys
-from pathlib import Path
 from unittest.mock import patch
 
 import pytest
 
-sys.path.insert(0, str(Path(__file__).resolve().parents[1] / "skills" / "last30days" / "scripts"))
-
 from lib.env import extract_browser_credentials, COOKIE_DOMAINS