Show unconfirmed USt-IdNr. in red, auto-select the field on blur

Makes the "konnte nicht bestätigt werden" message read as an actual
error instead of neutral status text, and re-focuses + selects the
whole VAT ID on an unconfirmed result — the customer almost certainly
needs to retype it, so the next keystroke should just replace it
outright.

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

app/checkout/components/CheckoutContent.tsx

@@ -354,7 +354,8 @@ export function CheckoutContent({
   // wherever vatExemptPreview/exemptTotalsPreview are computed below — a
   // validated German VAT ID never zero-rates a domestic sale).
   async function handleVatIdBlur(e: React.FocusEvent<HTMLInputElement>) {
-    const value = e.target.value;
+    const input = e.target;
+    const value = input.value;
     const formatError = validateVatIdFormat(value);
     setFieldError("vatId", formatError);
     if (!value.trim() || formatError) {
@@ -374,6 +375,14 @@ export function CheckoutContent({
         return;
       }
       setVatIdViesStatus(data.valid ? "valid" : "invalid");
+      // Re-focus + select the whole value on an unconfirmed VAT ID — the
+      // customer almost certainly needs to retype it (a typo, or the
+      // wrong id entirely), so the next keystroke should just replace it
+      // outright rather than requiring a manual select-all first.
+      if (!data.valid) {
+        input.focus();
+        input.select();
+      }
     } catch {
       setVatIdViesStatus("unavailable");
     }
@@ -732,7 +741,9 @@ export function CheckoutContent({
                       {isExemptionEligibleCountry(buyerDestinationCountry) ? " — Lieferung wird steuerfrei berechnet." : "."}
                     </span>
                   )}
-                  {vatIdViesStatus === "invalid" && "USt-IdNr. konnte nicht bestätigt werden."}
+                  {vatIdViesStatus === "invalid" && (
+                    <span className="text-red-600">USt-IdNr. konnte nicht bestätigt werden.</span>
+                  )}
                   {vatIdViesStatus === "unavailable" && "USt-IdNr.-Prüfung derzeit nicht möglich."}
                 </p>
               </div>