The app has no backend, so a share link embeds the whole radar as
base64url in the query string. Opening /share?d=... validates and
imports a fresh copy into the recipient's radars, then opens it.
A Radar gains an optional Concept — a short subtitle naming the product
and its typical performances, rendered under the title and wrapping to a
balanced second line when long. Old radars default to an empty Concept
on load.
