Show product subline on cards/cart/PDP hero; brand-color trailing period

Follows Products.subline (docker/payload commit ad7156e). Cards and cart
line items showed nothing but the bare name — added the subline under it.
der-eine and todo-cards' hero taglines were hardcoded copy nearly
identical to this new field — switched both to read subline instead, so
future edits go through the CMS.

Also adds a shared ProductName component: every hand-written PDP headline
already styled a trailing "." in brand color, but the few places that
render product.name as plain text (cards, cart, the Payload-driven
tasse-die-pause hero) had silently lost that styling. Centralizes it so
it can't drift per call site again.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01J1Hu5bZ1kZUgKhab6yNwCt

app/todo-cards/components/TodoKartenHero.tsx

@@ -97,12 +97,14 @@ export async function TodoKartenHero() {
               >
                 ToDo-Karten<span className="text-brand">.</span>
               </p>
-              <p
-                className="font-semibold text-h3 text-text-primary"
-                style={{ fontFamily: "var(--font-lora)" }}
-              >
-                Kleine Karten. Große Wirkung.
-              </p>
+              {product?.subline && (
+                <p
+                  className="font-semibold text-h3 text-text-primary"
+                  style={{ fontFamily: "var(--font-lora)" }}
+                >
+                  {product.subline}
+                </p>
+              )}
             </div>
 
             <p className="text-body text-text-body">