Move Settings out of the menu-bar popover into a standalone resizable AppKit
window so clicking it no longer steals focus and dismisses the bar (the .sheet
inside MenuBarExtra(.window) was the root cause). Force the actual NSWindow
appearance (aqua/darkAqua/system) on both the popover and the settings window
so Light/Dark visibly flips materials and semantic colors, not just custom
tokens. Replace the fragile popover quit dialog with an inline two-step
arm/confirm. Widen the dropdown and increase spacing/type for readability. Fill
the settings window responsively and make Done close it via the window
controller (dismiss() is a no-op in a hosted NSWindow).
