L14 Abrechnungsübersicht: Backoffice-Übersicht, Detail, Druckansicht, Meilensteine im Auftrag und mobil, API

/billing mit Tabs Offen/Abgerechnet/Storniert, Filtern und Mehrfachdruck; /billing/[id] mit Abrechnungsblatt und Aktionen (abgerechnet mit Rechnungsnummer, PDF, Rechnungsnummer ändern, stornieren); /billing/print; Auftrags-Tab „Meilensteine & Abrechnung“; mobiler Abschnitt „Erreicht melden“ (offline); Dashboard-Kachel „Bereit zur Abrechnung“; /api/v1/billing*, Meilenstein-Endpunkte und OpenAPI.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/app/(app)/work-orders/[id]/page.tsx

@@ -16,6 +16,7 @@ import {
   ReportsTab,
   TimesTab,
 } from "@/components/work-orders/detail-tabs";
+import { WorkOrderBillingTab } from "@/components/billing/work-order-billing-tab";
 import { pageContext } from "@/components/work-orders/page-context";
 import { Field, inputCls, LinkTabs, StatusBadge } from "@/components/work-orders/ui";
 import { WorkOrderFields } from "@/components/work-orders/work-order-fields";
@@ -28,7 +29,7 @@ import { customerDisplayName, customerOption, teamOptions, userOptions } from "@
 import { listOrderTypes } from "@/server/services/work-orders/settings";
 import { reasonRequired } from "@/server/services/work-orders/transition";
 
-const TABS = ["overview", "checklist", "material", "times", "photos", "notes", "reports", "documents", "history"] as const;
+const TABS = ["overview", "checklist", "material", "times", "photos", "notes", "reports", "billing", "documents", "history"] as const; // L14: billing
 type Tab = (typeof TABS)[number];
 type SP = Record<string, string | string[] | undefined>;
 const one = (v: string | string[] | undefined) => (Array.isArray(v) ? v[0] : v);
@@ -198,6 +199,7 @@ export default async function WorkOrderDetailPage({ params, searchParams }: { pa
             }
           />
         )}
+        {tab === "billing" && <WorkOrderBillingTab ctx={ctx} wo={wo} locale={locale} tz={tz} />}
         {tab === "documents" && <DocumentsTab {...tabProps} uploadError={one(sp.uploadError)} uploaded={one(sp.uploaded) === "1"} />}
         {tab === "history" && <HistoryTab {...tabProps} />}
       </div>