Address review feedback: deduplicate query_type, clean unused imports, fix defaults

- Remove duplicate detect_query_type from query.py (divergent 5-type version);
  canonical 7-type version lives in query_type.py
- Fix reddit.py import to use query_type.detect_query_type
- Clean unused STOPWORDS/SYNONYMS/tokenize imports from youtube_yt, instagram,
  tiktok, scrapecreators_x, bird_x after relevance consolidation
- Fix _relevance_filter default from 0.7 to 0.0 (items without relevance
  should not silently pass the filter)
- Remove --dateafter from yt-dlp (returns 0 results for evergreen topics)
- Remove restrictSearchableAttributes from HN search (misses Ask/Show HN)
- Lower HN points filter from >5 to >2 (avoids filtering niche posts)
- Add error logging to select_openai_model HTTP failures
- Remove mise.toml and internal planning doc from repo
- Update module docstrings to describe current purpose, not migration history
- Update tests to import from canonical relevance module

tests/test_youtube_relevance.py

@@ -7,7 +7,7 @@ from pathlib import Path
 # Add lib to path
 sys.path.insert(0, str(Path(__file__).parent.parent / "scripts"))
 
-from lib.youtube_yt import _compute_relevance, _tokenize
+from lib.relevance import token_overlap_relevance as _compute_relevance, tokenize as _tokenize
 
 
 class TestTokenize(unittest.TestCase):