refactor(frontend): each page fills the floating header itself; the header knows no page

The header used to pick its pills by `page === …` and import five module controls, and Plex's
Discover/Browse toggle needed a context bridge to reach the sub-view that lives in PlexBrowse.
Now the header is an empty band: PageShell hands its root box out as a slot, a page portals its
own pills into it (PageHeader), and the palette's Jump-to pill shows where no page does
(PageHeaderDefault, rendered inside the page's Suspense so a loading page shows no stand-in).
Plex's toggles take the sub-view as a prop; PlexViewBridge and its context are gone, and with
them the header's five layer suppressions.

No visible change: every header pill's box measured identical against the previous build on eight
pages, in Hungarian and English.

frontend/src/modules/plex/PlexHeader.tsx

@@ -0,0 +1,19 @@
+import { PageHeader } from "../../components/ui/PageShell";
+import PlexSearchBox from "./PlexSearchBox";
+import PlexScopeToggle from "./PlexScopeToggle";
+import PlexViewToggle from "./PlexViewToggle";
+import type { PlexViewControls } from "./plexSubUrl";
+
+// Plex's pills in the floating header: the search box, then the library scope (movie/show/both, plus
+// the playlists/collections surfaces) and the Discover ⟷ Browse switch — relocated here from the
+// filter sidebar so the primary "what am I browsing" controls are always in reach. Both toggles drive
+// PlexBrowse's sub-view, which PlexBrowse hands down as `view`.
+export default function PlexHeader({ view }: { view: PlexViewControls }) {
+  return (
+    <PageHeader>
+      <PlexSearchBox />
+      <PlexScopeToggle view={view} />
+      <PlexViewToggle view={view} />
+    </PageHeader>
+  );
+}