The Settings window inherited the base `.modal` vertical centering
(`align-items:center`). Its height is content-driven, so every tab is a
different height — and a vertically centered window grows and shrinks
around its own midpoint, making the in-modal nav rail (and the whole
window) appear to jump vertically when switching between pages.
Top-anchor the Settings window on desktop (`align-items:flex-start` plus
a fixed `margin-top`) so the top edge stays put and the panel only ever
grows downward. Scoped to desktop only — on mobile the panel is a
full-height bottom sheet that is already stable. Opening and dragging the
window both clear the inline margin/top, so window placement is otherwise
unchanged.
Fixes#208
62c60fc484