Release v1.4.0 - Full emoji support and HTML rendering engine

Major new features:
- Full emoji support via HTML/Chromium rendering engine
- Table of contents generation with [TOC] marker
- Automatic page numbering in footer
- Dual-engine architecture (HTML default, ReportLab legacy)
- Improved Mermaid diagram sizing and quality

Technical improvements:
- New html_renderer.py module for Playwright-based rendering
- Mermaid diagrams auto-sized to fit pages (75% height limit)
- Page numbers via Playwright footer template
- HTML engine now default with --engine parameter
- ReportLab still available for advanced PDF features

Updates:
- README.md completely rewritten for v1.4.0
- CLI default changed from reportlab to html engine
- Export convert_markdown_to_pdf_html in __init__.py
- Updated pyproject.toml description

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: claude