fix: TypeScript error in InfoCard icon variant check

Fix TypeScript build error "Type 'null' cannot be used as an index type"
by adding explicit null check for variant before indexing defaultIcons.

The variant from VariantProps can be null even with a default value,
so TypeScript requires an explicit check.

Changes:
- Added null check: showDefaultIcon && variant
- Added 'as const' to defaultIcons for better type inference

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/components/InfoCard.tsx

@@ -103,9 +103,10 @@ function InfoCard({
     warning: ExclamationTriangleIcon,
     error: ExclamationTriangleIcon,
     success: CheckCircleIcon,
-  };
+  } as const;
 
-  const Icon = CustomIcon || (showDefaultIcon ? defaultIcons[variant] : null);
+  const Icon =
+    CustomIcon || (showDefaultIcon && variant ? defaultIcons[variant] : null);
 
   return (
     <div className={cn(infoCardVariants({ variant }), className)} {...props}>