fix: preserve viewport mode during trackpad scroll

[DjDeveloperr]

Summary

• Keep wheel/trackpad scrolling on the simulator canvas from forcing the viewport into manual mode.
• Preserve the active fit or center zoom state when the wheel gesture is only panning, while still allowing manual zoom to pan normally.
• Add focused unit coverage for the wheel/pan decision logic.

Testing

• npm run --prefix client test -- viewportWheel.test.ts
• npm run --prefix client test
• npm run --prefix client typecheck
• npm run --prefix client build
• Local browser QA against the client confirmed fit and center remained active after wheel scrolling, with no console errors in the page startup path.