feat: Add PDF and image export functionality

[akonan]

Summary

• Implements PDF export capability with customizable page sizes and orientation (Issue Add PDF export renderer #38)
• Adds PNG, SVG, JPEG, and WebP image export support with high-DPI scaling (Issue Add PNG/SVG image export #39)
• Uses Puppeteer as an optional dependency for rendering

Features Added

PDF Export (Issue #38)

• Generate PDF from HTML renderer output using Puppeteer
• Support for custom page sizes (A4, A3, Letter, Legal, Tabloid)
• Landscape/portrait orientation options
• All visual styles fully supported

Image Export (Issue #39)

• PNG export with configurable dimensions
• SVG scalable vector graphics output
• JPEG export with quality control
• WebP modern format support
• High-DPI support with device scale factor (2x, 3x)
• Optional transparent backgrounds for PNG

CLI Enhancements

# PDF export
wiremd design.md --format pdf -o design.pdf --page-size A3 --landscape

# Image exports
wiremd design.md --format png --width 1920 --height 1080 --scale 2
wiremd design.md --format svg -o design.svg
wiremd design.md --format jpeg -o design.jpg
wiremd design.md --format webp -o design.webp

Technical Details

• Added src/renderer/pdf-renderer.ts for PDF generation
• Added src/renderer/image-renderer.ts for image exports
• Updated CLI to support new format options and parameters
• Configured Vite to exclude Puppeteer from bundling
• Puppeteer is installed as an optional dependency

Testing

All export formats have been tested with:

• Different visual styles (sketch, clean, wireframe, material, etc.)
• Various page sizes and orientations for PDF
• Different resolutions and scale factors for images
• Complex wireframe layouts

Documentation

• Updated README with comprehensive export documentation
• Added usage examples for all new export formats
• Documented Puppeteer requirement for export features

Closes

• Closes Add PDF export renderer #38
• Closes Add PNG/SVG image export #39

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