fix: improve inline code contrast in AI chat responses

bg-white/[0.08] was too subtle — text was unreadable against the dark
background. Bump to bg-white/[0.12] with a subtle border and
text-foreground for proper contrast.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/ui/MarkdownContent.tsx

@@ -54,7 +54,7 @@ export function MarkdownContent({ content, className }: MarkdownContentProps) {
           }
           return (
             <code
-              className="rounded bg-white/[0.08] px-1.5 py-0.5 font-mono text-sm text-secondary"
+              className="rounded bg-white/[0.12] border border-white/[0.06] px-1.5 py-0.5 font-mono text-sm text-foreground"
               {...props}
             >
               {children}