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_evaluator_v3.py

@@ -1,13 +1,10 @@
 import json
 import os
-import sys
 import tempfile
 import unittest
 from pathlib import Path
 from unittest import mock
 
-sys.path.insert(0, str(Path(__file__).resolve().parents[1] / "skills" / "last30days" / "scripts"))
-
 import evaluate_search_quality as evaluator
 
 
@@ -202,6 +199,5 @@ class EvaluatorV3Tests(unittest.TestCase):
             self.assertIn("| topic a | 0.10 | 0.30 |", summary)
             self.assertEqual("HEAD~1", metrics["baseline"])
 
-
 if __name__ == "__main__":
     unittest.main()