perf(ui): a next-page fetch joins the one in flight instead of sending the cursor again

react-query's fetchNextPage cancels a next page still loading and sends it again by default.
Our requests ignore the abort signal, so the server ran both: the feed's read-ahead effect
re-runs on scroll frames before isFetchingNextPage reaches it, and on prod every feed page
went out 2-3 times (a 0.8 s title sort queued to 2.3 s). Every call now passes NEXT_PAGE
({cancelRefetch: false}), lint-enforced, with a contract test.

frontend/src/components/AdminLogs.tsx

@@ -13,6 +13,7 @@ import { api, type LogFacet, type LogQuery, type ServerLogRow } from "../lib/api
 import { copyText } from "../lib/clipboard";
 import { formatDateTimeSec } from "../lib/format";
 import { nextNavId, notifyNav, rememberNavPosition } from "../lib/history";
+import { NEXT_PAGE } from "../lib/nextPage";
 import { LEVEL_GROUPS, type LevelGroup } from "../lib/log";
 import {
   DEFAULT_LOGS_STATE,
@@ -156,7 +157,7 @@ export default function AdminLogs() {
           ? "countsFailed"
           : null;
   const retryFailed = () => {
-    if (logs.isFetchNextPageError) void logs.fetchNextPage();
+    if (logs.isFetchNextPageError) void logs.fetchNextPage(NEXT_PAGE);
     else if (logs.isError) void logs.refetch();
     if (facets.isError) void facets.refetch();
   };
@@ -190,7 +191,7 @@ export default function AdminLogs() {
 
   const loadOlder = () => {
     setLive(false);
-    void logs.fetchNextPage();
+    void logs.fetchNextPage(NEXT_PAGE);
   };
 
   const copy = async () => {