Move low-stock hint to badge, right-align VAT breakdown, gate cart discount field, split billing/shipping delivery method

- Removed the inline "Nur noch wenige verfügbar" text hint from
  AddToCartButton/AddToCartInlineButton (was making card heights vary in
  every grid that renders them — RelatedProducts, ProductSpotlight's CTA
  row) — now only shown via the same image-overlaid pill badge
  Ausverkauft/discount already use (position: absolute, doesn't affect
  layout). Added that badge to RelatedProducts.tsx and todo-cards'
  Pricing.tsx, which didn't have it before.
- RelatedProducts cards now also show "inkl. X% MwSt." (was missing
  entirely)
- VatBreakdown rows are now flex rows with a spacer instead of plain
  text, so every € amount right-aligns to the same edge regardless of
  how many digits the rate itself has (was visibly staggered with mixed
  7%/19% rates)
- Cart's manual discount-code field only renders when Payload actually
  has at least one active code right now (lib/discountServer.ts's new
  hasActiveDiscountCode()) — no point showing an open field that could
  never validate. An already-applied code (e.g. from an older session)
  still always shows its own result row regardless.
- Checkout's "1. Rechnungsadresse" no longer offers a Packstation option
  — a Packstation isn't a valid billing address for an invoice. Only a
  plain street address now; Packstation is only offered on the separate,
  optional "Abweichende Lieferadresse" section, which already had its own
  address/Packstation toggle.

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

app/components/AddToCartButton.tsx

@@ -18,7 +18,6 @@ export function AddToCartButton({
   className,
   productId = "todo-karten",
   outOfStock = false,
-  lowStock = false,
   variants = [],
 }: {
   label: string;
@@ -30,9 +29,6 @@ export function AddToCartButton({
   /** Product-level — only meaningful when `variants` is empty, same split as
    * AddToCartInlineButton. */
   outOfStock?: boolean;
-  /** Product-level low-stock hint, same "only meaningful without variants"
-   * split as outOfStock. */
-  lowStock?: boolean;
   /** Optional — same shape/semantics as AddToCartInlineButton's own
    * `variants` prop; all three callers already fetch the full product
    * server-side, so this is just threaded straight through. */
@@ -47,7 +43,6 @@ export function AddToCartButton({
   useEffect(() => () => clearTimeout(timeoutRef.current), []);
 
   const currentlyOutOfStock = variants.length > 0 ? (variants.find((v) => v.name === selectedVariant)?.outOfStock ?? false) : outOfStock;
-  const currentlyLowStock = variants.length > 0 ? (variants.find((v) => v.name === selectedVariant)?.lowStock ?? false) : lowStock;
 
   function handleClick() {
     if (currentlyOutOfStock) return;
@@ -81,7 +76,17 @@ export function AddToCartButton({
   const displayLabel = currentlyOutOfStock ? "Ausverkauft" : label;
 
   return (
-    <div className="flex flex-col gap-1">
+    // Low stock is deliberately NOT surfaced here as its own text line
+    // (it used to be) — that made this block's height vary card-to-card
+    // in every grid that renders this component, breaking equal-height
+    // card alignment (ProductSpotlight's CTA row, RelatedProducts' grid).
+    // The image-overlaid pill badge (ProductGrid.tsx/ProductSpotlight.tsx/
+    // RelatedProducts.tsx, position: absolute, doesn't participate in
+    // layout flow) is the one place this now shows, same as
+    // Ausverkauft/discount already do. The variant-select suffix below is
+    // unaffected — a native <select>'s own height doesn't vary with its
+    // option text.
+    <div className="flex flex-col gap-2">
       {variants.length > 0 && (
         <select
           value={selectedVariant}
@@ -97,9 +102,6 @@ export function AddToCartButton({
           ))}
         </select>
       )}
-      {currentlyLowStock && !currentlyOutOfStock && (
-        <p className="text-label font-bold text-warning">Nur noch wenige verfügbar</p>
-      )}
       <button
         ref={buttonRef}
         type="button"