Use design system --primary var for Algolia highlight colors

Replaces hardcoded hsl(347 ...) values with var(--primary) from
@arcadeai/design-system tokens and color-mix() for transparent tints.
Dark mode text override removed since --primary resolves identically
in both modes.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: teallarson

app/globals.css

@@ -160,17 +160,16 @@ nav > div:has(.algolia-search-button) {
 /* Algolia search hit highlight — brand red */
 .ais-Highlight-highlighted,
 .ais-Snippet-highlighted {
-  background: hsl(347 100% 50% / 0.15);
-  color: hsl(347 100% 45%);
+  background: color-mix(in oklch, var(--primary) 15%, transparent);
+  color: var(--primary);
   border-radius: 2px;
   font-style: normal;
   font-weight: 600;
 }
 
 .dark .ais-Highlight-highlighted,
 .dark .ais-Snippet-highlighted {
-  background: hsl(347 100% 50% / 0.2);
-  color: hsl(347 100% 65%);
+  background: color-mix(in oklch, var(--primary) 20%, transparent);
 }
 
 /* Override Nextra code highlight colors to use green instead of red */