fix(mobile): add native-feeling touch gestures for SheetsViewer

- Implement hybrid touch overlay for swipe-to-scroll and pinch-to-zoom
- Add iOS-like scroll physics with velocity sampling and momentum threshold
- Slow drags stop immediately, fast flicks apply momentum
- Pinch zoom using Univer Facade API with CSS transform fallback
- Hide scrollbars for cleaner mobile experience
- Tap detection for future cell selection support

Author: typelets