feat(offers,invoices): per-currency 'Celkem' totals beneath the lists (consistent with orders)

Mirrors the orders totals exactly: /stats (offers) + /list-totals (issued +
received invoices) endpoints sum each doc's total per currency across the active
filter (reusing extracted where-builders so they stay in sync with the lists),
rendered as the identical 'Celkem: …' block via the shared formatMultiCurrency.
Existing invoice/received KPI stats untouched.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/admin/lib/queries/offers.ts

@@ -1,6 +1,11 @@
 import { queryOptions } from "@tanstack/react-query";
 import { jsonQuery, paginatedJsonQuery } from "../apiAdapter";
 
+export interface CurrencyAmount {
+  amount: number;
+  currency: string;
+}
+
 export interface ItemTemplate {
   id: number;
   name: string;
@@ -91,6 +96,27 @@ export const offerListOptions = (filters: {
     },
   });
 
+export const offerStatsOptions = (filters: {
+  search?: string;
+  status?: string;
+  customer_id?: number;
+}) =>
+  queryOptions({
+    queryKey: ["offers", "stats", filters],
+    queryFn: async () => {
+      const params = new URLSearchParams();
+      if (filters.search) params.set("search", filters.search);
+      if (filters.status) params.set("status", filters.status);
+      if (filters.customer_id)
+        params.set("customer_id", String(filters.customer_id));
+      const qs = params.toString();
+      const data = await jsonQuery<{ totals?: CurrencyAmount[] }>(
+        `/api/admin/offers/stats${qs ? `?${qs}` : ""}`,
+      );
+      return data.totals ?? [];
+    },
+  });
+
 export interface OfferItemData {
   id?: number;
   description: string;