modernise website, keep terminal theme

[debo]

Refresh of the site keeping the green-on-black terminal identity (same palette, monospace, ./ title, >> markers).

What changed:

• responsive layout, hero with a terminal window, section cards for install/usage/deps
• copy buttons on every code block, keyboard focus states, prefers-reduced-motion handled
• content updated to current install flow (phpenv plugin + standalone), https clone URLs, PHP 8.3 examples, refreshed build deps
• dropped the dead ga.js analytics, the GitHub-generator params.json, and unused bkg.png/blacktocat.png
• core team updated; full MIT license kept on the page behind a disclosure

Preview locally:

git switch modernise-website-1785104510
python3 -m http.server 8000

then open http://localhost:8000 (copy buttons need localhost or https to work)

Opening as draft for the team to sign off before it goes live.