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/pages/Offers.tsx

@@ -13,12 +13,21 @@ import { useAuth } from "../context/AuthContext";
 import Forbidden from "../components/Forbidden";
 
 import apiFetch from "../utils/api";
-import { formatCurrency, formatDate, czechPlural } from "../utils/formatters";
+import {
+  formatCurrency,
+  formatDate,
+  formatMultiCurrency,
+  czechPlural,
+} from "../utils/formatters";
 import useTableSort from "../hooks/useTableSort";
 import useDebounce from "../hooks/useDebounce";
 import { useQuery, useQueryClient } from "@tanstack/react-query";
 import { usePaginatedQuery } from "../hooks/usePaginatedQuery";
-import { offerListOptions, offerCustomersOptions } from "../lib/queries/offers";
+import {
+  offerListOptions,
+  offerStatsOptions,
+  offerCustomersOptions,
+} from "../lib/queries/offers";
 import { useApiMutation } from "../lib/queries/mutations";
 import {
   Button,
@@ -370,6 +379,16 @@ export default function Offers() {
     }),
   );
 
+  // Per-currency total over the WHOLE filtered set (not one page). Uses the
+  // SAME filters as the list query so the summary matches what's shown.
+  const statsQuery = useQuery(
+    offerStatsOptions({
+      search: debouncedSearch,
+      status: statusFilter || undefined,
+      customer_id: customerFilter || undefined,
+    }),
+  );
+
   // Mark first load done in an effect (not during render) to avoid a
   // render-phase ref mutation.
   useEffect(() => {
@@ -875,6 +894,27 @@ export default function Offers() {
             )
           }
         />
+        {(statsQuery.data?.length ?? 0) > 0 && (
+          <Box
+            sx={{
+              display: "flex",
+              justifyContent: "flex-end",
+              mt: 1.5,
+              px: 1,
+              gap: 1,
+              color: "text.secondary",
+              fontSize: "0.9rem",
+            }}
+          >
+            <span>Celkem:</span>
+            <Box
+              component="span"
+              sx={{ fontWeight: 700, color: "text.primary" }}
+            >
+              {formatMultiCurrency(statsQuery.data ?? [])}
+            </Box>
+          </Box>
+        )}
         <Pagination
           page={page}
           pageCount={pagination?.total_pages ?? 1}