Generate invoice PDFs attached to order confirmation, and send emails on order status changes

Invoice PDFs (§14 UStG line items, tenant-configurable VAT rate) are now
generated at checkout and attached to the confirmation email, plus
available on demand from the order-detail page. Payload-side, orders now
also email the customer on shipped/cancelled/return_requested/returned,
with Stornorechnung/Gutschrift correction PDFs attached for the latter two
so the original invoice's immutable number stays honest.

app/lib/payload.ts

@@ -604,7 +604,13 @@ export async function getLegalPage(type: LegalPageType, options?: { draft?: bool
   };
 }
 
-export type EmailTemplateType = "order-confirmation" | "password-reset";
+export type EmailTemplateType =
+  | "order-confirmation"
+  | "password-reset"
+  | "order-shipped"
+  | "order-cancelled"
+  | "order-return-requested"
+  | "order-returned";
 
 type PayloadEmailTemplate = {
   type: EmailTemplateType;
@@ -636,3 +642,35 @@ export async function getEmailTemplate(
   const data: { docs?: PayloadEmailTemplate[] } = await res.json();
   return data.docs?.[0] ?? null;
 }
+
+export type InvoiceSettings = {
+  sellerName: string;
+  sellerStreet: string;
+  sellerZip: string;
+  sellerCity: string;
+  sellerCountry: string;
+  sellerEmail: string;
+  vatId: string;
+  taxRatePercent: number;
+  bankDetails: string | null;
+};
+
+// Server-only in practice (only ever called from app/lib/invoiceData.ts),
+// but kept in this file rather than a "use server"-only module since every
+// other Payload fetcher lives here too — no client component imports it.
+// invoice-settings' read access is admin-only plus this same service
+// secret (see InvoiceSettings.ts) — it holds bank details, not something
+// to leave publicly readable like Products/ShippingSettings.
+export async function getInvoiceSettings(): Promise<InvoiceSettings | null> {
+  const params = new URLSearchParams({ "where[tenant.slug][equals]": TENANT_SLUG, limit: "1" });
+  const res = await fetch(`${PAYLOAD_URL}/api/invoice-settings?${params}`, {
+    headers: { "x-order-service-secret": process.env.ORDER_SERVICE_SECRET || "" },
+    cache: "no-store",
+  });
+  if (!res.ok) {
+    console.error(`getInvoiceSettings: Payload returned ${res.status} ${res.statusText}`);
+    return null;
+  }
+  const data: { docs?: InvoiceSettings[] } = await res.json();
+  return data.docs?.[0] ?? null;
+}