Compact the heading type scale and stop iOS focus zoom

Move the document title to step +5 and section headings to step +3 so
headings sit closer to the compact interface. On coarse pointers, text
fields and the document editor read at no less than 16px so iOS Safari
does not zoom the page when one is focused.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>