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_version.py

@@ -5,13 +5,10 @@ to SKILL.md frontmatter. These tests use monkeypatch to swap the render module's
 __file__ attribute, which controls where the walk starts.
 """
 
-import sys
 import unittest
 from pathlib import Path
 from unittest.mock import patch
 
-sys.path.insert(0, str(Path(__file__).resolve().parents[1] / "skills" / "last30days" / "scripts"))
-
 from lib import render
 
 
@@ -132,6 +129,5 @@ class SkillVersionFallbackTests(unittest.TestCase):
         with patch.object(render, "__file__", str(fake_render)):
             self.assertEqual("5.5.5", render._skill_version())
 
-
 if __name__ == "__main__":
     unittest.main()