Three changes to improve heading quality:
1. Raise heading threshold from 1.1x to 1.2x base font size, reducing
false positives where slightly larger body text was promoted to headers.
2. Add word count guard (max 15 words) to skip heading detection for
long body paragraphs that happen to use a larger font.
3. Add merge_heading_lines() preprocessing that joins consecutive lines
at the same heading level on the same page (e.g., "About Glenair,
the Mission-Critical" + "Interconnect Company" → single heading).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
