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_bird_x.py

@@ -2,16 +2,12 @@ import json
 import os
 import shutil
 import subprocess
-import sys
 import textwrap
 import unittest
 from pathlib import Path
 
-sys.path.insert(0, str(Path(__file__).resolve().parents[1] / "skills" / "last30days" / "scripts"))
-
 from lib.bird_x import parse_bird_response
 
-
 REPO_ROOT = Path(__file__).resolve().parents[1]
 VENDORED_BIRD = REPO_ROOT / "skills" / "last30days" / "scripts" / "lib" / "vendor" / "bird-search" / "bird-search.mjs"
 
@@ -31,7 +27,6 @@ class TestBirdXEngagementZero(unittest.TestCase):
         self.assertEqual(0, items[0]["engagement"]["likes"])
         self.assertEqual(5, items[0]["engagement"]["reposts"])
 
-
 @unittest.skipUnless(shutil.which("node"), "node is required for vendored Bird tests")
 class TestVendoredBirdRuntime(unittest.TestCase):
     def test_check_uses_env_credentials_without_browser_cookie_dependency(self):
@@ -305,6 +300,5 @@ class TestRunBirdSearchJsonDecodeRetry(unittest.TestCase):
         self.assertEqual(response, timeout_error)
         mock_sleep.assert_not_called()
 
-
 if __name__ == "__main__":
     unittest.main()