feat(customers): add initial admin bootstrap and csv import

frontend/athena/app/api/customers/import/template/route.ts

@@ -0,0 +1,40 @@
+import { NextResponse } from "next/server";
+
+const columns = [
+  "customer_number",
+  "company_name",
+  "legal_name",
+  "customer_type",
+  "status",
+  "industry",
+  "website",
+  "email",
+  "phone",
+  "tax_number",
+  "vat_id",
+  "notes",
+  "address_type",
+  "street",
+  "postal_code",
+  "city",
+  "state",
+  "country",
+  "address_is_primary",
+  "contact_first_name",
+  "contact_last_name",
+  "contact_position",
+  "contact_email",
+  "contact_phone",
+  "contact_mobile",
+  "contact_is_primary",
+  "contact_notes",
+];
+
+export async function GET() {
+  return new NextResponse(`${columns.join(";")}\n`, {
+    headers: {
+      "Content-Disposition": 'attachment; filename="kundenimport-vorlage.csv"',
+      "Content-Type": "text/csv; charset=utf-8",
+    },
+  });
+}