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_youtube_relevance.py

@@ -1,11 +1,8 @@
 """Tests for YouTube relevance scoring."""
 
-import sys
 import unittest
-from pathlib import Path
 
 # Add lib to path
-sys.path.insert(0, str(Path(__file__).parent.parent / "skills" / "last30days" / "scripts"))
 
 from lib.relevance import token_overlap_relevance as _compute_relevance, tokenize as _tokenize
 
@@ -105,6 +102,5 @@ class TestComputeRelevance(unittest.TestCase):
         result = _compute_relevance("Seedance", "Random cooking video")
         self.assertEqual(result, 0.0)
 
-
 if __name__ == "__main__":
     unittest.main()