The default fontSize (13px) was too small after DemoViewport's CSS
zoom (~0.84), rendering at ~10.9px on screen — nearly identical to
the original 11px. Bump default to 14px so it renders at ~11.8px.

Add maxWidth prop to constrain and centre the terminal shell within
wide viewports. Without this, 40–60 char terminal lines leave the
right half of an 896px viewport empty.

Made-with: Cursor