Give the tech radar its own page

/radar (/en/radar, /ca/radar) shows every technology the collective has
placed, by ring: logo, category, what it is, why it sits there, its
website and how many projects use it. The landing's radar summary links
to it.

It is the first listing — a page this site composes rather than one
record's — so resolveRoute learns about those (LISTINGS), and builds
their addresses and hreflang alternates from the same table.

Logos sit on a light tile in both themes. A brand's mark is not ours to
recolour, and Rust's, which is black, would vanish in dark mode.

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

README.md

@@ -225,6 +225,12 @@ named in that language:
 /colabora/frontend     /en/contribute/frontend  /ca/col-labora/frontend
 ```
 
+Besides records there are **listings**, pages this site composes itself —
+the tech radar at `/radar`, `/en/radar`, `/ca/radar` (`LISTINGS`). A panel page
+with the same slug would be shadowed by one, so they are few and deliberately
+named. Radar logos sit on a light tile in both themes: a brand's mark is not
+ours to recolour, and some (Rust's, black) would vanish in dark mode.
+
 `core/routes.ts#resolveRoute` is that rule read backwards, and its `SECTIONS`
 mirror the API's `config/site.php` (`paths`) — a change there has to be made
 here too. `/es/…` is not a shape the API produces, so a record has one address