- check_verbatim now computes n-gram overlap for BOTH question_text and
correct_option vs source texts, returning max(question_ratio, option_ratio).
Extracted _ngram_overlap_ratio helper for reuse.
- Added 4 missing blacklist patterns: 'this segment', 'this frame',
'the current frame', 'frame summary'.
- Added 5 new test cases covering the above changes.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>