Three fixes for better table extraction from spreadsheet-exported PDFs:
1. Convert thin filled rects (< 2pt) to PdfLine objects before line-based
table detection. Many PDFs draw table borders as narrow filled rectangles
instead of stroked paths — these were invisible to the line detector.
2. Relax uniform row spacing rejection (CV 0.05 → 0.02). Spreadsheet
exports have very even row heights that were being rejected as "chart
grids".
3. Fix continuation row merging: don't merge rows where the only non-first
cell content is a long label (section headers like "Category No. 03").
Don't merge first-cell-only rows with long text ("Note: ...").
Also adds multi-Y row splitting in line-based detection and column-aware
table detection skipping for multi-column pages.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
