Scroll the sideways card rows with a plain wheel

[mobrava]

Description

Scrolling vertically over the card row, a pinboard row, or the tab strip now moves it sideways. Those rows only run horizontally, so a wheel that only reports vertical movement did nothing and Shift had to be held.

A scroll that is already sideways is left alone, so Shift + wheel, a thumb wheel, and trackpad sideways gestures are unchanged, and a view that also scrolls vertically keeps the normal meaning of the wheel. The event's vertical movement is moved onto the horizontal axis and handed back to AppKit, which keeps its line height, acceleration, and edge clamping instead of reimplementing them.

The choice comes from the direction of the scroll rather than the kind of device. A mouse reports the same fine deltas a trackpad does once its vendor software enables smooth scrolling, so treating precise deltas as "this is a trackpad, leave it alone" would skip exactly the mice this is meant to fix. Within one gesture the first decision is held until momentum finishes, so a swipe that drifts off axis cannot flip between sideways and vertical frame by frame.

Covers the scrolling request in #26. The Simplified Chinese settings localization and the hover based Quick Look target in that issue are untouched, so it stays open.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Refactoring (no functional changes)
• Documentation update
• Other (please describe):

How to Test

bash scripts/test-and-launch.sh

Then, with the panel open and enough clips to overflow the row:

1. Scroll the wheel over the cards. The row moves sideways, in the direction the rest of the system scrolls.
2. Scroll over a pinboard row and over the tab strip when it overflows.
3. Hold Shift and scroll, and confirm it behaves as it did before.
4. Open Quick Look on an image at actual size and confirm the wheel still moves it up and down.

docs/testing/issue-26-wheel-scroll.md has the full matrix.

Checklist

• I have tested this change on macOS 15+
• The project builds without warnings (xcodegen generate && xcodebuild)
• I have followed the existing code style and conventions
• I have updated documentation if needed

[mobrava]

Merged into main as e8aff17. Squashed locally rather than through the button so the commit author stays consistent with the rest of the history.