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/_footer.scss

@@ -1,6 +1,6 @@
 .wg-footer {
 	margin-top: 1.25rem;
-	border-top: 1px solid rgba(194, 163, 90, 0.16);
+	border-top: 1px solid rgba(var(--wg-gold-rgb), 0.16);
 	color: var(--wg-text-muted);
 	background:
 		linear-gradient(180deg, rgba(13, 9, 18, 0), rgba(8, 5, 12, 0.76)),
@@ -123,7 +123,7 @@
 	width: min(100%, var(--wg-page-width));
 	margin: 0 auto;
 	padding: 1.375rem clamp(1rem, 4vw, 2rem);
-	border-top: 1px solid rgba(194, 163, 90, 0.1);
+	border-top: 1px solid rgba(var(--wg-gold-rgb), 0.1);
 
 	p {
 		margin: 0;
@@ -164,9 +164,9 @@
 
 	&:hover,
 	&:focus {
-		border-color: rgba(194, 163, 90, 0.22);
+		border-color: rgba(var(--wg-gold-rgb), 0.22);
 		color: var(--wg-text-soft);
-		background: rgba(194, 163, 90, 0.06);
+		background: rgba(var(--wg-gold-rgb), 0.06);
 	}
 
 	&:focus-visible {