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_skill_meta.py

@@ -6,15 +6,13 @@ regex coverage inside the helper could pass CI because render.py's fallback
 to "?" swallows the signal.
 """
 
-import sys
 import tempfile
 import unittest
 from pathlib import Path
 
+from lib.skill_meta import read_skill_version
 
 ROOT = Path(__file__).resolve().parents[1]
-sys.path.insert(0, str(ROOT / "skills" / "last30days" / "scripts"))
-from lib.skill_meta import read_skill_version  # noqa: E402
 
 
 class ReadSkillVersionTests(unittest.TestCase):
@@ -56,6 +54,5 @@ class ReadSkillVersionTests(unittest.TestCase):
         path.write_bytes(bytes(range(128, 256)))
         self.assertIsNone(read_skill_version(path))
 
-
 if __name__ == "__main__":
     unittest.main()