Support exporting multiple PDF pages into a single composite image

[timhaintz]

Problem

When working with GitHub Copilot Chat, there is a hard 20-image conversation limit. Even with selective page attachment, many papers still have more important pages than can fit comfortably under that limit.

In many cases, users would prefer to combine multiple PDF pages into one stitched image so that, for example, 4 pages count as 1 attached image.

Proposed solution

Add a new export mode that renders multiple selected pages into a single composite image.

Possible shapes:

• A new command such as PDF Toolkit: Screenshot Composite...
• A new option inside the existing Custom Screenshot wizard

Expected behavior

• User selects pages or ranges (e.g. 1-4)
• Extension renders those pages into one image instead of separate files
• Support common layouts:
  • vertical stack
  • 2x2 grid
  • optional spacing or page labels
• Output to PNG at the selected resolution

Why this matters

This would be very useful for AI-assisted analysis of papers, reports, and technical documents where users want to fit more content under Copilot's image limit.

Example:

• Pages 1-4 become one composite PNG
• Pages 5-8 become another
• A 16-page section could be shared in 4 images instead of 16

Nice-to-have options

• Automatic pagination into multiple composite images when too many pages are selected
• Optional page-number overlays
• Optional background color and padding
• Optional maximum image height/width to avoid giant files