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_ui_v3.py

@@ -1,13 +1,8 @@
-# ruff: noqa: E402
 import io
-import sys
 import unittest
 from contextlib import redirect_stderr
-from pathlib import Path
 from unittest import mock
 
-sys.path.insert(0, str(Path(__file__).resolve().parents[1] / "skills" / "last30days" / "scripts"))
-
 from lib import ui
 
 
@@ -72,6 +67,5 @@ class UiV3Tests(unittest.TestCase):
         self.assertIn("Truth Social: 1 post", output)
         self.assertIn("Xiaohongshu: 4 posts", output)
 
-
 if __name__ == "__main__":
     unittest.main()