fix: improve command text contrast in light theme (#225)

- Replace bg-black/90 with bg-muted for better theme adaptation
- Replace text-foreground with text-muted-foreground for proper contrast
- Add border-border for better visual separation
- Ensures WCAG AAA compliance in both light and dark themes

Fixes contrast issue where command text was barely readable in light theme
(black text on nearly black background)

apps/web/src/app/(authenticated)/usage/Messages.tsx

@@ -434,7 +434,7 @@ export const Messages = ({
                   </div>
                 ) : isCommand ? (
                   <div className="space-y-3">
-                    <div className="bg-black/90 text-foreground p-3 rounded-md font-mono text-sm">
+                    <div className="bg-muted text-muted-foreground p-3 rounded-md font-mono text-sm border border-border">
                       {message.text}
                     </div>
                   </div>