Updates add-layout-preprocessing proposal:
- Auto mode: analyze image quality, auto-select parameters
- Manual mode: user override with specific settings
- Preview API: compare original vs preprocessed before processing
- Frontend UI: mode selection, manual controls, preview button
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
Problem: PP-Structure misses tables with faint lines/borders
Solution: Preprocess images (contrast, sharpen) for layout detection
- Preprocessed image only used for layout detection
- Original image preserved for element extraction (quality)
Includes: proposal.md, design.md, tasks.md, spec delta
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
