feat(ST-507): add code-helpers and CodeBadge component

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

components/shared/code-badge.tsx

@@ -0,0 +1,20 @@
+import { cn } from '@/lib/utils'
+
+interface CodeBadgeProps {
+  code: string | null | undefined
+  className?: string
+}
+
+export function CodeBadge({ code, className }: CodeBadgeProps) {
+  if (!code) return null
+  return (
+    <span
+      className={cn(
+        'inline-flex items-center rounded-md border border-border bg-surface-container px-1.5 py-0.5 font-mono text-[11px] leading-none text-muted-foreground',
+        className,
+      )}
+    >
+      {code}
+    </span>
+  )
+}