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_rerank_fun.py

@@ -1,13 +1,7 @@
 """Tests for the fun judge heuristic fallback in rerank.py."""
 
-import sys
-from pathlib import Path
-
 import pytest
 
-SCRIPTS_DIR = Path(__file__).parent.parent / "skills" / "last30days" / "scripts"
-sys.path.insert(0, str(SCRIPTS_DIR))
-
 from lib import schema
 from lib.rerank import _apply_single_fun_fallback, _extract_comment_text