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_signals_v3.py

@@ -1,9 +1,5 @@
 import math
-import sys
 import unittest
-from pathlib import Path
-
-sys.path.insert(0, str(Path(__file__).resolve().parents[1] / "skills" / "last30days" / "scripts"))
 
 from lib import schema, signals
 from lib.hackernews import parse_hackernews_response
@@ -232,7 +228,6 @@ class SignalsV3Tests(unittest.TestCase):
         pruned = signals.prune_low_relevance([weak], minimum=0.1)
         self.assertEqual(["weak"], [item.item_id for item in pruned])
 
-
     # -- Iteration 1: HN engagement bug --
 
     def test_hackernews_parse_emits_comments_key(self):
@@ -566,7 +561,6 @@ class SignalsV3Tests(unittest.TestCase):
         self.assertIn("social", ids, "Item with relevance 0.05 should survive pruning")
         self.assertIn("strong", ids)
 
-
     # -- Unit 3: YouTube high-engagement relevance floor --
 
     def test_youtube_high_engagement_gets_relevance_floor(self):
@@ -608,7 +602,6 @@ class SignalsV3Tests(unittest.TestCase):
         rel = signals.local_relevance(item, "kanye west")
         self.assertLess(rel, 0.3, f"Non-YouTube item should not get YouTube floor, got {rel}")
 
-
     # -- Unit 8: Engagement floor for TikTok/Instagram --
 
     def test_tiktok_below_1000_views_pruned(self):
@@ -709,6 +702,5 @@ class SignalsV3Tests(unittest.TestCase):
         aspire_ids = [item.item_id for item in pruned if item.item_id.startswith("aspire")]
         self.assertEqual(len(aspire_ids), 0, f"All @aspiresnippets items should be pruned, got {aspire_ids}")
 
-
 if __name__ == "__main__":
     unittest.main()