feat: Initial implementation of Annas Rechnungsmanager

Full-stack German accounting & invoice management web application:

- Multi-company management (Mandantenverwaltung) with full CRUD
- Invoice creation with dynamic line items and automatic tax calculation
- Sequential invoice numbering per company (RE-2024-001 format)
- §14 UStG compliant PDF invoice generation via @react-pdf/renderer
- Customer management (Kundenverwaltung) per company
- Tax reports: quarterly USt-Voranmeldung and monthly revenue overview
- Email/password authentication via NextAuth.js v5
- Responsive, modern UI with Tailwind CSS and custom shadcn/ui components
- Prisma v5 ORM with MySQL/MariaDB schema + demo seed data

Stack: Next.js 14 (App Router) · TypeScript · Prisma/MySQL · NextAuth.js

https://claude.ai/code/session_01FN53KKxo5ebrGwqFhxzkT9

src/app/(dashboard)/companies/[id]/invoices/new/invoice-form-client.tsx

@@ -0,0 +1,30 @@
+"use client";
+
+import { useRouter } from "next/navigation";
+import { InvoiceForm } from "@/components/invoice/invoice-form";
+
+interface Props {
+  customers: { id: string; name: string }[];
+  companyId: string;
+}
+
+export function InvoiceFormClient({ customers, companyId }: Props) {
+  const router = useRouter();
+
+  async function handleSubmit(data: Record<string, unknown>) {
+    const res = await fetch("/api/invoices", {
+      method: "POST",
+      headers: { "Content-Type": "application/json" },
+      body: JSON.stringify(data),
+    });
+
+    if (res.ok) {
+      const invoice = await res.json();
+      router.push(`/companies/${companyId}/invoices/${invoice.id}`);
+    } else {
+      alert("Fehler beim Erstellen der Rechnung.");
+    }
+  }
+
+  return <InvoiceForm customers={customers} companyId={companyId} onSubmit={handleSubmit} />;
+}