prototype(#53): palette candidates as runtime token swaps

Throwaway. Tokenises the theme's literal colours so candidate palettes can be
swapped in the browser, adds three candidates (Plum Noir one-metal, two-metal
pewter, two-metal plus a champagne inset), a WCAG checker, a seeder and the
screenshots they are judged on.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

scss/westgate/_search.scss

@@ -7,7 +7,7 @@
 	letter-spacing: 0.09em;
 	text-transform: uppercase;
 	color: var(--wg-gold);
-	background: rgba(194, 163, 90, 0.1);
+	background: rgba(var(--wg-gold-rgb), 0.1);
 	border: 1px solid var(--wg-ledger-border);
 	vertical-align: middle;
 }