Honor Products.noShippingCost across cart, checkout, and product pages

- api/checkout/route.ts: authoritative shipping charge is 0 whenever
  every cart line opts out via noShippingCost, regardless of the
  free-shipping threshold.
- Cart/checkout order summaries: the whole "Versand" line (cost, free-
  shipping note, delivery time) is hidden entirely rather than showing
  "Kostenlos" — that's a different state from hitting the threshold.
- ProductSpotlight/Pricing/TodoKartenHero: "zzgl. Versand" and delivery-
  time hints drop for an exempted product's own page.
- /versand + its shared modal: one clarifying sentence that digital
  products are exempt.
- Widerrufsformular link: opens inline in a new tab (no forced download),
  arrow icon changed from a download glyph to a plain right arrow to
  match.

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

app/todo-cards/components/Pricing.tsx

@@ -97,10 +97,19 @@ export async function Pricing() {
               )}
               <p className="font-bold text-h3 text-text-primary">{formatPrice(product.price)}</p>
             </div>
-            <p className="text-label text-text-muted">{kleinunternehmer ? "zzgl. Versand" : `inkl. ${taxRate}% MwSt. zzgl. Versand`}</p>
-            <p className="text-label text-text-muted">
-              Lieferzeit: {shipping.totalDays.min}–{shipping.totalDays.max} Werktage innerhalb Deutschlands
-            </p>
+            {(() => {
+              const priceHint = kleinunternehmer
+                ? product.noShippingCost
+                  ? null
+                  : "zzgl. Versand"
+                : `inkl. ${taxRate}% MwSt.${product.noShippingCost ? "" : " zzgl. Versand"}`;
+              return priceHint && <p className="text-label text-text-muted">{priceHint}</p>;
+            })()}
+            {!product.noShippingCost && (
+              <p className="text-label text-text-muted">
+                Lieferzeit: {shipping.totalDays.min}–{shipping.totalDays.max} Werktage innerhalb Deutschlands
+              </p>
+            )}
           </div>
           {/* Single product, no grid siblings to stay equal-height with —
               plain conditional line, same reasoning as ProductSpotlight.tsx. */}

app/todo-cards/components/TodoKartenHero.tsx

@@ -124,12 +124,21 @@ export async function TodoKartenHero() {
                     <p className="text-body text-text-muted line-through">{formatPrice(product.compareAtPrice!)}</p>
                   )}
                   <p className="font-bold text-h3 text-text-primary">{formatPrice(product.price)}</p>
-                  <p className="text-label text-text-muted">{kleinunternehmer ? "zzgl. Versand" : `inkl. ${taxRate}% MwSt. zzgl. Versand`}</p>
+                  {(() => {
+                    const priceHint = kleinunternehmer
+                      ? product.noShippingCost
+                        ? null
+                        : "zzgl. Versand"
+                      : `inkl. ${taxRate}% MwSt.${product.noShippingCost ? "" : " zzgl. Versand"}`;
+                    return priceHint && <p className="text-label text-text-muted">{priceHint}</p>;
+                  })()}
                 </div>
               )}
-              <p className="text-label text-text-muted">
-                Lieferzeit: {shipping.totalDays.min}–{shipping.totalDays.max} Werktage innerhalb Deutschlands
-              </p>
+              {!product?.noShippingCost && (
+                <p className="text-label text-text-muted">
+                  Lieferzeit: {shipping.totalDays.min}–{shipping.totalDays.max} Werktage innerhalb Deutschlands
+                </p>
+              )}
               {/* Single product, no grid siblings to stay equal-height with —
                   plain conditional line, same reasoning as ProductSpotlight.tsx/Pricing.tsx. */}
               {anyLowStock && <p className="text-label font-bold text-warning">Nur noch wenige verfügbar</p>}