feat(preview): move around the sheet with mouse dragging

[Go2Engle]

Summary

Move around the sheet preview by dragging empty space with the left mouse button, or by holding the right mouse button and dragging anywhere, including over a selected card. This makes zoomed-in sheets easier to navigate while preserving card selection and artwork inspection.

Type of change

• Feature
• Bug fix
• Refactor
• Documentation
• Infrastructure/CI

Technical details

• Pan the existing preview viewport without changing card placement or print output.
• Capture the mouse pointer so dragging continues outside the preview; stop on release, cancellation, capture loss, or window blur.
• Keep ordinary card clicks, keyboard activation, touch input, and native scrollbar interactions available. Suppress context menus and accidental clicks during panning.
• Measure movement from the drag origin to avoid accumulated rounding drift, and show a grabbing cursor while dragging.
• Add six interaction regression tests and update the feature reference, Cricut workflow guide, and README workflow.

Testing performed

All 188 tests pass after rebasing onto current main; the production build, formatting, and diff checks pass.

npm test
npm run build
npx prettier --check src/lib/artboard-pan.ts tests/artboard-pan.test.ts src/App.tsx src/style.css
git diff --check origin/main...HEAD

Browser checks verified left dragging on empty space and paper margins, right dragging over a selected card without changing selection, release outside the preview, context-menu suppression, the grabbing cursor, scroll-wheel zoom, and normal card clicks opening artwork inspection.

Breaking changes

None.

Checklist

• The PR title follows Conventional Commits.
• I ran npm test and npm run build.
• I added or updated tests for behavior changes.
• I updated documentation for user-facing changes.
• I updated the README workflow; the existing feature summary and screenshot remain applicable.
• I did not manually edit release versions or CHANGELOG.md.