Herdr.app: setting for mouse wheel scroll speed in terminal panes

[fidelisakilan]

Herdr.app has no setting for how far the mouse wheel scrolls in terminal panes.

I use LinearMouse, and its scroll speed suits webpages and other apps. Terminals feel too fast at that speed, so I set mouse-scroll-multiplier = precision:0.5,discrete:0.5 in Ghostty. Now I run Claude Code inside Herdr.app, and Ghostty's setting doesn't apply, so scrolling back through agent output overshoots.

The herdr CLI already has ui.mouse_scroll_lines. I'd like a similar setting in Herdr.app's settings.json, ideally a multiplier that accepts fractions (like Ghostty's) and can be set separately for trackpad (precision) and mouse wheel (discrete) scrolling.

Environment: Herdr.app 0.1.12, hc 0.1.17, macOS 27.0.1, LinearMouse.

(Moved from #5761, which I filed as a bug by mistake.)