Add shared query.py and relevance.py modules

Consolidate duplicated _extract_core_subject() (7 copies across bird_x,
reddit, youtube_yt, tiktok, instagram, bluesky, scrapecreators_x) into
query.extract_core_subject() with parameterized noise set, max_words,
and suffix stripping.

Consolidate duplicated _tokenize/_compute_relevance/STOPWORDS/SYNONYMS
(4 copies across youtube_yt, tiktok, instagram, scrapecreators_x) into
relevance.token_overlap_relevance() with hashtag-aware matching.

Integration into per-module imports follows in next commits.

tests/test_query.py

@@ -0,0 +1,130 @@
+"""Tests for query.py — shared query utilities."""
+
+import sys
+import unittest
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).parent.parent / "scripts"))
+
+from lib.query import NOISE_WORDS, extract_core_subject
+
+
+class TestExtractCoreSubject(unittest.TestCase):
+    """Tests for extract_core_subject() with default noise set."""
+
+    def test_strips_what_are_prefix(self):
+        self.assertEqual(extract_core_subject("what are the best AI tools"), "ai")
+
+    def test_strips_how_to_prefix(self):
+        self.assertEqual(extract_core_subject("how to use cursor IDE"), "cursor ide")
+
+    def test_strips_what_do_people_think(self):
+        result = extract_core_subject("what do people think about React Server Components")
+        self.assertEqual(result, "react server components")
+
+    def test_preserves_product_name(self):
+        self.assertEqual(extract_core_subject("cursor IDE"), "cursor ide")
+
+    def test_strips_trailing_punctuation(self):
+        result = extract_core_subject("what is Claude?")
+        self.assertFalse(result.endswith("?"))
+
+    def test_empty_string(self):
+        self.assertEqual(extract_core_subject(""), "")
+
+    def test_all_noise_returns_original(self):
+        # When all words are noise, fall back to original text
+        result = extract_core_subject("best latest new")
+        self.assertTrue(len(result) > 0)
+
+    def test_only_first_prefix_stripped(self):
+        # "how to" should match, stripping once, not recursively
+        result = extract_core_subject("how to use how to debug")
+        self.assertIn("debug", result)
+
+
+class TestMaxWords(unittest.TestCase):
+    """Tests for max_words parameter."""
+
+    def test_max_words_caps_output(self):
+        result = extract_core_subject(
+            "multi agent reinforcement learning framework",
+            max_words=5,
+        )
+        self.assertLessEqual(len(result.split()), 5)
+
+    def test_max_words_none_no_cap(self):
+        result = extract_core_subject("cursor IDE react native components")
+        # Without max_words, no cap applied
+        self.assertGreaterEqual(len(result.split()), 3)
+
+    def test_max_words_fallback_on_empty(self):
+        # All words filtered + max_words should fall back to original
+        result = extract_core_subject("best top latest", max_words=3)
+        self.assertTrue(len(result) > 0)
+
+
+class TestStripSuffixes(unittest.TestCase):
+    """Tests for strip_suffixes parameter."""
+
+    def test_strips_best_practices(self):
+        result = extract_core_subject(
+            "claude code best practices",
+            strip_suffixes=True,
+        )
+        self.assertNotIn("practices", result)
+
+    def test_strips_use_cases(self):
+        result = extract_core_subject(
+            "react hooks use cases",
+            strip_suffixes=True,
+        )
+        self.assertNotIn("cases", result)
+
+    def test_no_strip_without_flag(self):
+        result = extract_core_subject("claude code best practices")
+        # "best" and "practices" are noise words so they get filtered anyway
+        # but the suffix phase doesn't run
+        self.assertIn("claude", result)
+
+
+class TestCustomNoise(unittest.TestCase):
+    """Tests for noise override parameter."""
+
+    def test_custom_noise_keeps_tips(self):
+        # YouTube keeps tips/tricks/tutorial — pass a noise set without them
+        youtube_noise = frozenset({
+            'best', 'top', 'good', 'great', 'awesome', 'killer',
+            'latest', 'new', 'news', 'update', 'updates',
+            'trending', 'hottest', 'popular', 'viral',
+            'practices', 'features',
+            'recommendations', 'advice',
+            'prompt', 'prompts', 'prompting',
+            'methods', 'strategies', 'approaches',
+        })
+        result = extract_core_subject("best react tips", noise=youtube_noise)
+        self.assertIn("tips", result)
+
+    def test_default_noise_removes_tips(self):
+        result = extract_core_subject("best react tips")
+        self.assertNotIn("tips", result)
+
+
+class TestNoiseWordsCompleteness(unittest.TestCase):
+    """Verify NOISE_WORDS superset covers all platform sets."""
+
+    def test_question_words_present(self):
+        for w in ('who', 'why', 'when', 'where', 'does', 'should', 'could', 'would'):
+            self.assertIn(w, NOISE_WORDS, f"Missing question word: {w}")
+
+    def test_core_filler_present(self):
+        for w in ('the', 'a', 'an', 'is', 'are', 'for', 'with', 'about'):
+            self.assertIn(w, NOISE_WORDS)
+
+    def test_research_meta_present(self):
+        for w in ('best', 'top', 'latest', 'trending', 'popular'):
+            self.assertIn(w, NOISE_WORDS)
+
+
+if __name__ == "__main__":
+    unittest.main()