fix: support pinch-to-zoom and drag-to-pan in lightbox

[Cao1224]

Hi @Bilb — this is my first contribution to this project. I've fixed #701 by adding pinch-to-zoom and drag-to-pan to the Lightbox image viewer. Would appreciate a review when you have time!

First time contributor checklist:

• I have read the README and Contributor Guidelines

Contributor checklist:

• My commits are in nice logical chunks with good commit messages
• My changes are rebased on the latest dev branch
• A yarn ready run passes successfully (more about tests here)
• My changes are ready to be shipped to users

Description

Adds pinch-to-zoom and drag-to-pan to the Lightbox image viewer. Images containing text are often difficult to read at fit-to-screen size, requiring users to download and open them externally to inspect the content.

How it works:

• Pinch or Ctrl+scroll to zoom in and out toward the pointer position
• Drag to pan while zoomed
• Double-click to reset to fit-to-screen
• Zoom and pan reset automatically when navigating to the next or previous image
• Video and unsupported file types are unaffected

Manual testing performed:

• Pinch-to-zoom on Mac trackpad — zooms toward pointer
• Ctrl+scroll on Mac — zooms in and out
• Drag while zoomed — pans without closing the lightbox
• Double-click — resets to fit-to-screen from any zoom level
• Click dark background — closes the lightbox at any zoom level
• Click image without dragging — lightbox stays open
• Navigate prev/next — zoom resets on each new image
• Video attachments — no change in behavior

No new automated tests added — the meaningful behavior (gesture feel, pointer anchoring, click vs drag distinction) is covered by manual testing above.

OS tested: macOS [14.8.7]