feat(checkout): add Packstation delivery option

Toggle between "Lieferadresse" and "Packstation" in the checkout
address form. Packstation swaps Straße und Hausnummer for
Packstationnummer + Postnummer — there's no house number for a
Packstation, so the field doesn't apply.

app/checkout/components/CheckoutContent.tsx

@@ -71,6 +71,7 @@ export function CheckoutContent({
   const [shippingMethodId, setShippingMethodId] = useState<number | null>(shippingMethods[0]?.id ?? null);
   const [paymentMethodId, setPaymentMethodId] = useState<number | null>(paymentMethods[0]?.id ?? null);
   const [versandOpen, setVersandOpen] = useState(false);
+  const [deliveryMethod, setDeliveryMethod] = useState<"address" | "packstation">("address");
 
   const productsLoading = products.length === 0 && cart.length > 0;
   const items = cart
@@ -176,13 +177,67 @@ export function CheckoutContent({
               autoComplete="email"
               wrapperClassName="w-full sm:w-[calc(50%-0.5rem)] sm:flex-none min-w-0"
             />
-            <FormField
-              label="Straße und Hausnummer"
-              type="text"
-              placeholder="Musterstraße 1"
-              autoComplete="street-address"
-              wrapperClassName="w-full sm:w-[calc(50%-0.5rem)] sm:flex-none min-w-0"
-            />
+            {/* Segmented control, same sm:w-[calc(50%-0.5rem)] half-row
+                width as the field(s) below it — Lieferadresse keeps
+                Straße und Hausnummer, Packstation swaps it out for
+                Packstationnummer + Postnummer (DHL's two Packstation
+                identifiers; there's no house number to give). */}
+            <div className="w-full sm:w-[calc(50%-0.5rem)] flex flex-col gap-2 items-start">
+              <span className="text-label text-text-muted">Lieferart</span>
+              <div className="flex w-full rounded-sm border border-border overflow-hidden">
+                <button
+                  type="button"
+                  onClick={() => setDeliveryMethod("address")}
+                  aria-pressed={deliveryMethod === "address"}
+                  className={`flex-1 py-3 text-body-sm font-bold transition-colors ${
+                    deliveryMethod === "address"
+                      ? "bg-brand text-text-primary"
+                      : "text-text-muted hover:text-text-primary"
+                  }`}
+                >
+                  Lieferadresse
+                </button>
+                <button
+                  type="button"
+                  onClick={() => setDeliveryMethod("packstation")}
+                  aria-pressed={deliveryMethod === "packstation"}
+                  className={`flex-1 py-3 text-body-sm font-bold border-l border-border transition-colors ${
+                    deliveryMethod === "packstation"
+                      ? "bg-brand text-text-primary"
+                      : "text-text-muted hover:text-text-primary"
+                  }`}
+                >
+                  Packstation
+                </button>
+              </div>
+            </div>
+
+            {deliveryMethod === "address" ? (
+              <FormField
+                label="Straße und Hausnummer"
+                type="text"
+                placeholder="Musterstraße 1"
+                autoComplete="street-address"
+                wrapperClassName="w-full sm:w-[calc(50%-0.5rem)] sm:flex-none min-w-0"
+              />
+            ) : (
+              <div className="flex flex-col sm:flex-row gap-4 w-full">
+                <FormField
+                  label="Packstationnummer"
+                  type="text"
+                  inputMode="numeric"
+                  placeholder="123"
+                  autoComplete="off"
+                />
+                <FormField
+                  label="Postnummer"
+                  type="text"
+                  inputMode="numeric"
+                  placeholder="1234567"
+                  autoComplete="off"
+                />
+              </div>
+            )}
             <div className="flex flex-col sm:flex-row gap-4 w-full">
               <FormField label="PLZ" type="text" placeholder="10115" autoComplete="postal-code" />
               <FormField label="Ort" type="text" placeholder="Berlin" autoComplete="address-level2" />