Fix BuyNowButton disabled prop being silently ignored

[J8118]

Summary

In BuyNowButton.tsx line 69, the disabled attribute uses ?? (nullish coalescing) with loading on the left side:

disabled={loading ?? (passthroughProps as {disabled?: boolean}).disabled}

Since loading is a boolean (always true or false, never null or undefined), the right side is never evaluated. The consumer's disabled prop is silently ignored. Compare this to AddToCartButton which correctly combines conditions with ||.

File changed:

• packages/hydrogen-react/src/BuyNowButton.tsx (line 69)

Before:

disabled={loading ?? (passthroughProps as {disabled?: boolean}).disabled}

After:

disabled={loading || (passthroughProps as {disabled?: boolean}).disabled}

[fredericoo]

good spot - since `loading` is `useState(false)`, it's always a boolean and `??` never falls through. the consumer's `disabled` prop was being silently ignored.

this is a behavioural change though - consumers passing `disabled={true}` will now have it respected when `loading` is `false`. could you add a changeset? since this touches `hydrogen-react`, it also needs a companion hydrogen bump (hydrogen re-exports everything from hydrogen-react):

```md

"@shopify/hydrogen-react": patch
"@shopify/hydrogen": patch

Fixed BuyNowButton to respect the consumer's `disabled` prop when not in a loading state. Previously, the nullish coalescing operator (`??`) prevented the fallback from ever being evaluated since `loading` is always a boolean.
```

cheers!

[J8118]

Done — just pushed the changeset with the hydrogen-react + hydrogen bump