- Add detect_line_direction() function using unicode_bidi::bidi_class
- Count L (LTR) vs R/AL (RTL) characters, return dominant direction
- Default to Ltr for empty/neutral-only strings (per bead acceptance criteria)
- Return Mixed only when LTR and RTL counts are tied (both > 0)
- Add comprehensive tests for Latin, Arabic, Hebrew, Cyrillic, and edge cases
- Fix header_footer test: remove nonexistent reading_order_rank field
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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