Flag emoji (regional-indicator) do not render on Windows and several
Safari/WebKit configs, breaking the 'In 42+ languages' table there.
Replace each emoji with a local SVG <img> from flag-icons (MIT), served
from docs/assets/flags/ so the language selector renders everywhere.
Also convert the 5 'Document | Description' reference tables to definition
lists — full-width and scroll-free on GitHub (tables are capped at
width:max-content and scroll horizontally on narrow viewports).
