fix: remove conflicting default export guidance in react instructions

Author: pomfrida

.github/instructions/react.instructions.md

@@ -61,7 +61,7 @@ export const MyComponent: React.FC<MyComponentProps> = ({
 
 - Components should be composable and nestable
 - Avoid tightly coupled dependencies
-- Export both default and named exports when appropriate
+- Use named exports only (see global coding standards)
 - Keep components focused and simple
 - Implement error boundaries for error handling