docs: replace the before/after text blocks with terminal cards, add the Pi npm route

The two panels are now SVG terminal windows rather than a blockquote and
a fenced block. SVG rather than PNG so they stay crisp at any DPI, weigh
about 1KB and 2KB, and remain diffable in git. The canvas is 560 wide
rather than 760 so a phone scales them by roughly 64% instead of 46%,
which keeps the injected plan legible at 390px. GitHub's max-width rule
does the rest, so neither one can overflow the page.

Quick Install now also carries the Pi route, `pi install
npm:planning-with-files`, which was previously documented only further
down in the commands section, and the route table gains its row.