[BUG] Mouse Wheel Horizontal Scroll not working

**Describe the bug**
Shift + Scroll wheel did not Scroll horizontally for me in Chrome.

**To Reproduce**
Steps to reproduce the behavior:
1. Open a diagram in Chrome
2. Hold Shift key on keyboard and move scroll wheel
3. Diagram doesn't move

**Expected behavior**
Diagram should scroll horizontally

**Screenshots**
n/a

**Desktop (please complete the following information):**
- OS: macOS 26.6.1
- Browser: Chrome Version 151.0.7922.110 (Official Build) (arm64)

**Additional context**
Vertical scrolling with the mouse wheel works fine.

Start by reproducing the issue in Chrome with a diagram, holding Shift while using the mouse wheel, and inspect the diagram editor's wheel and horizontal-scrolling entry points. Done means vertical scrolling still works and Shift plus the wheel moves the diagram horizontally.

Written by the indexing model from the issue text.