feat(plex): fix the title-count row, scroll only the poster grid

Lift Plex browse's title-count line into the shell's fixed band via
PageToolbar, so the count stays visible while only the poster grid scrolls
(the filters already live in the left rail). Verified with a 3.5k-title
library: the count holds at a fixed offset while the grid scrolls. Suite
15/15, tsc + knip clean.

frontend/src/components/PlexBrowse.tsx

@@ -33,6 +33,7 @@ import { useHistorySubview } from "../lib/history";
 import { DetailCustomizeMenu, Filterable, useArtBackdrop, useDetailPrefs } from "../lib/plexDetailUi";
 import PlexPlaylistAdd, { type PlexAddTarget } from "./PlexPlaylistAdd";
 import PlexCollectionEditor from "./PlexCollectionEditor";
+import { PageToolbar } from "./PageShell";
 
 // Lazy: the rich player (pulls in hls.js) loads only when something is first played.
 const PlexPlayer = lazy(() => import("./PlexPlayer"));
@@ -286,9 +287,15 @@ export default function PlexBrowse({
 
   return (
     <div className="p-4 max-w-[1600px] mx-auto">
-      <p className="text-xs text-muted mb-3">
+      {/* The title count is fixed chrome — it portals into the shell's fixed band so it stays put
+          while only the poster grid scrolls. */}
+      <PageToolbar>
+        <div className="px-4 pt-3 pb-1 max-w-[1600px] mx-auto">
+          <p className="text-xs text-muted">
         {browseQ.isLoading ? " " : dq ? t("plex.searchCount", { count: total }) : t("plex.count", { count: total })}
-      </p>
+          </p>
+        </div>
+      </PageToolbar>
 
       {browseQ.isLoading ? (
         <p className="text-muted text-sm">{t("plex.loading")}</p>