Fix money rounding drift, low-stock hint spacing, spotlight CTA height mismatch

- Round subtotal/discountAmount/total to 2 decimals before persisting an
  order — float arithmetic on money was drifting into values like
  84.30000000000001, invisible wherever a display already ran it through
  toFixed(2), but stored as-is and visible raw in the Payload admin's
  plain number field
- Low-stock hint now uses gap-1 consistently (was gap-2) in both
  AddToCartButton/AddToCartInlineButton, for smaller/consistent spacing
  above it regardless of context
- ProductSpotlight's CTA row now uses items-start at sm: — without it,
  default cross-axis stretch made "Mehr erfahren" grow to match
  AddToCartButton's height whenever the low-stock hint made that one
  taller, so the link visibly looked "fatter" than the actual button

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/components/AddToCartInlineButton.tsx

@@ -77,7 +77,7 @@ export function AddToCartInlineButton({
       : "border-border hover:border-brand";
 
   return (
-    <div className="flex flex-col gap-2 w-full">
+    <div className="flex flex-col gap-1 w-full">
       {variants.length > 0 && (
         <select
           value={selectedVariant}