fix(ui): review round 2 — reveal floor, failed next page, count states, row Play

- DataTable: the reveal floor holds only in the view it was made for (Channels
  never clears its follow, so every later sort mounted rows up to it)
- Feed + Plex browse: a failed next page stops the read-ahead and shows a row
  that retries, instead of re-requesting it once a round-trip
- the YouTube Load more click uses nextPageOnClick; a contract pins NEXT_PAGE
  to the read-aheads and the click sites to nextPageOnClick
- ItemCount: a failed count says so; a stale one says updating to a screen reader
- the narrow-picture Play lift applies only where a hover row is there to clear
- PlayerModal: one description ladder for the popover and the panel, both tested
- plexImage contract reads every img src, any attribute order
- Tabs comment names who persists the sub-tab

frontend/src/components/Feed.tsx

@@ -7,7 +7,7 @@ import {
   useQueryClient,
 } from "@tanstack/react-query";
 import { qk } from "../lib/queryKeys";
-import { NEXT_PAGE } from "../lib/nextPage";
+import { nextPageOnClick } from "../lib/nextPage";
 import {
   ArrowLeft,
   Columns2,
@@ -557,7 +557,9 @@ export default function Feed({
               <div className="text-center pt-4">
                 <Button
                   variant="outline"
-                  onClick={() => void ytQuery.fetchNextPage(NEXT_PAGE)}
+                  onClick={() =>
+                    void ytQuery.fetchNextPage(nextPageOnClick(ytQuery.isFetchingNextPage))
+                  }
                   loading={ytQuery.isFetchingNextPage}
                 >
                   {ytQuery.isFetchingNextPage
@@ -710,7 +712,11 @@ export default function Feed({
       <div className="flex items-center gap-1.5 gap-y-2 flex-wrap">
         {/* The item count is the fixed leading element — a fixed-width pill so a changing number
             never shoves the controls beside it (see ItemCount). */}
-        <ItemCount count={summaryQuery.data?.count} stale={summaryQuery.isPlaceholderData} />
+        <ItemCount
+          count={summaryQuery.data?.count}
+          stale={summaryQuery.isPlaceholderData}
+          failed={summaryQuery.isError && !summaryQuery.data}
+        />
         <FilterFoldButton
           fold={fold}
           label={t("sidebar.filters")}
@@ -891,7 +897,10 @@ export default function Feed({
           onToggleSave={onToggleSave}
           onResetState={onResetState}
           onOpen={openVideo}
-          hasNextPage={!!hasNextPage}
+          // A failed next page stops the read-ahead: retry is off, and re-running on every settle would
+          // re-request it once a round-trip for as long as the end is in view (E31 review 2). The row
+          // below says so and retries on a click.
+          hasNextPage={!!hasNextPage && !query.isFetchNextPageError}
           isFetching={query.isFetching}
           fetchNextPage={fetchNextPage}
         />
@@ -910,6 +919,15 @@ export default function Feed({
       {isFetchingNextPage && (
         <div className="text-center text-muted py-4">{t("feed.loadingMore")}</div>
       )}
+      {query.isFetchNextPageError && !isFetchingNextPage && (
+        <StateMessage
+          tone="error"
+          compact
+          onRetry={() => void fetchNextPage(nextPageOnClick(isFetchingNextPage))}
+        >
+          {t("common.loadMoreFailed")}
+        </StateMessage>
+      )}
     </div>
   );
 }