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/lib/__tests__/cartTotals.test.ts

@@ -6,6 +6,7 @@ const product = (overrides: Partial<Product> = {}): Product => ({
   id: "todo-karten",
   numericId: 1,
   name: "ToDo-Karten",
+  subline: null,
   description: null,
   descriptionText: "",
   sku: null,

app/lib/payload.ts

@@ -181,6 +181,9 @@ export type Product = {
   // slug-based call site.
   numericId: number;
   name: string;
+  // Short tagline shown under the name on cards/cart/PDP hero — see
+  // Products.ts's own field comment. null/"" means show nothing extra.
+  subline: string | null;
   // Raw Lexical richText JSON — rendered formatted (bold/italic/multiple
   // paragraphs) on the PDP via the shared <RichText> component. Plain-text
   // consumers (Passend-dazu cards, JSON-LD) use `descriptionText` below
@@ -271,6 +274,7 @@ export type Product = {
 type PayloadProduct = {
   id: number;
   name: string;
+  subline: string | null;
   slug: string;
   description: unknown | null;
   sku: string | null;
@@ -356,6 +360,7 @@ export function mapPayloadProduct(product: PayloadProduct): Product {
     id: product.slug,
     numericId: product.id,
     name: product.name,
+    subline: product.subline || null,
     description: product.description ?? null,
     descriptionText: extractPlainText(descriptionRoot),
     sku: product.sku || null,