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_keychain.py

@@ -12,19 +12,15 @@ from __future__ import annotations
 
 import re
 import subprocess
-import sys
 from pathlib import Path
 from unittest import mock
 
 import pytest
 
-sys.path.insert(0, str(Path(__file__).resolve().parents[1] / "skills" / "last30days" / "scripts"))
-
-from lib import env  # noqa: E402
+from lib import env
 
 SETUP_KEYCHAIN_SH = Path(__file__).resolve().parents[1] / "skills" / "last30days" / "scripts" / "setup-keychain.sh"
 
-
 # ---------------------------------------------------------------------------
 # _load_keychain unit tests
 # ---------------------------------------------------------------------------
@@ -93,12 +89,10 @@ def test_load_keychain_skips_empty_stdout():
          mock.patch("subprocess.run", return_value=_run_result(0, "")):
         assert env._load_keychain(["XAI_API_KEY"]) == {}
 
-
 # ---------------------------------------------------------------------------
 # get_config integration tests
 # ---------------------------------------------------------------------------
 
-
 @pytest.fixture
 def clean_env(monkeypatch, tmp_path):
     """Hide every key get_config might touch and point CONFIG_FILE at a
@@ -154,7 +148,6 @@ def test_get_config_openai_key_can_come_from_keychain(clean_env):
     assert cfg["OPENAI_API_KEY"] == "sk-from-kc"
     assert cfg["OPENAI_AUTH_SOURCE"] == "api_key"
 
-
 # ---------------------------------------------------------------------------
 # Drift guard: lib/env.py KEYCHAIN_KEYS and setup-keychain.sh ALL_KEYS must
 # stay in lockstep. A mismatch means users storing a key via the helper script