fix(fiber): normalize viewport event prefixes

[raashish1601]

Summary

Canvas supports overriding pointer coordinate extraction via eventPrefix, but prefixes like client and page produce viewport/document coordinates instead of coordinates local to the canvas bounds. Those values were normalized directly against the canvas size, so an offset canvas produced shifted pointer coordinates and raycasts.

This normalizes clientX/clientY by the canvas bounds and pageX/pageY by the bounds plus window scroll. Offset-like prefixes keep their existing behavior.

Test Plan

• npx jest packages/fiber/tests/events.test.tsx --runInBand
• npx eslint packages/fiber/src/web/Canvas.tsx packages/fiber/tests/events.test.tsx
• npx prettier --check packages/fiber/src/web/Canvas.tsx packages/fiber/tests/events.test.tsx
• npm run -s typecheck
• npm run -s build

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