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/Feed.tsx

@@ -7,6 +7,7 @@ import {
   useQueryClient,
 } from "@tanstack/react-query";
 import { qk } from "../lib/queryKeys";
+import { NEXT_PAGE } from "../lib/nextPage";
 import {
   ArrowLeft,
   Columns2,
@@ -556,7 +557,7 @@ export default function Feed({
               <div className="text-center pt-4">
                 <Button
                   variant="outline"
-                  onClick={() => ytQuery.fetchNextPage()}
+                  onClick={() => void ytQuery.fetchNextPage(NEXT_PAGE)}
                   loading={ytQuery.isFetchingNextPage}
                 >
                   {ytQuery.isFetchingNextPage