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_html_render.py

@@ -1,17 +1,12 @@
-# ruff: noqa: E402
 """Tests for the HTML emit renderer."""
 
 from __future__ import annotations
 
-import sys
 import tempfile
 import unittest
 from html.parser import HTMLParser
 from pathlib import Path
 
-REPO_ROOT = Path(__file__).resolve().parents[1]
-sys.path.insert(0, str(REPO_ROOT / "skills" / "last30days" / "scripts"))
-
 import last30days as cli
 from lib import html_render, schema
 
@@ -297,6 +292,5 @@ class HtmlCliIntegrationTests(unittest.TestCase):
         self.assertIn("comparing 2: OpenClaw, Hermes", saved)
         self.assertNotIn("last30days · OpenClaw</title>", saved)
 
-
 if __name__ == "__main__":
     unittest.main()