Fix desktop/laptop touchscreen pan/zoom and touch interaction routing

[flooryyyy]

Note

PR used GPT 5.4. Submitted as draft in case of code review and refactoring.

Summary

This draft fixes the main desktop-touchscreen canvas issues:

• restores two-finger pinch zoom on the canvas
• restores one-finger canvas pan on empty space
• prevents canvas pan from competing with block-content scrolling
• keeps resize handles touch-owned
• moves the touch gesture handling onto pointer events so touch and pen follow the same event path
  React Flow uses

Details

The main change is a dedicated touch viewport handler for the editor canvas, plus narrower touch
routing:

• pane touches control canvas pan and pinch
• block-content touches stay with block scrolling/editing
• resize controls keep touch-action: none

Manual testing

Tested on a desktop touchscreen setup:

• two-finger pinch zoom works
• one-finger pan on empty canvas works
• scrolling inside scrollable block content no longer pans the canvas at the same time
• pen interactions still work for moving and resizing blocks

Notes

This is a draft because I’d like review on the touch-routing approach and any React Flow-specific
refinements before marking it ready.

Canvas pan, zoom, and scrolling work reliably with a touchscreen.

Moving or resizing blocks with finger input may still be inconsistent on some touchscreen devices due
to odd input behavior from touchscreens and how those events are interpreted. Moving and resizing with
a pen works correctly.

[3xpyth0n]

Opened reviewed & fixed PR in #64.