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_competitor_fanout.py

@@ -1,20 +1,14 @@
-# ruff: noqa: E402
 """Tests for scripts/lib/fanout.run_competitor_fanout."""
 
 from __future__ import annotations
 
 import io
-import sys
 import threading
 import time
 import unittest
 from contextlib import redirect_stderr
-from pathlib import Path
 from unittest import mock
 
-REPO_ROOT = Path(__file__).resolve().parents[1]
-sys.path.insert(0, str(REPO_ROOT / "skills" / "last30days" / "scripts"))
-
 from lib import fanout
 
 
@@ -155,6 +149,5 @@ class FanoutOrchestratorTests(unittest.TestCase):
             )
         self.assertEqual([label for label, _ in results], ["OpenAI"])
 
-
 if __name__ == "__main__":
     unittest.main()