fix: merge overlapping GestureHandler event handlers

[Mormentz]

Summary

• GestureHandler no longer lets consumer onTouch* / pointer props replace the gesture library handlers.
• Overlapping event handlers are composed (gesture first, then consumer) so swipe, pinch, and tap still fire.
• Adds Vitest coverage for baseline gestures, overlapping consumer handlers (including preventDefault), and non-event props.

Test plan

• pnpm exec vitest run src/components/mobile/__tests__/GestureHandler.test.tsx
• Confirm swipe/pinch still work when a parent also passes onTouchStart / onTouchMove / onTouchEnd

closes #1044

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