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_version_consistency.py

@@ -1,15 +1,12 @@
 import re
-import sys
 import unittest
 from pathlib import Path
 
+from lib.skill_meta import read_skill_version
 
 ROOT = Path(__file__).resolve().parents[1]
 SKILL_ROOT = ROOT / "skills" / "last30days"
 
-sys.path.insert(0, str(SKILL_ROOT / "scripts"))
-from lib.skill_meta import read_skill_version  # noqa: E402
-
 
 def _skill_version() -> str:
     version = read_skill_version(SKILL_ROOT / "SKILL.md")
@@ -77,6 +74,5 @@ class TestVersionConsistency(unittest.TestCase):
 
         self.assertEqual([], offenders)
 
-
 if __name__ == "__main__":
     unittest.main()