feat(player): the YouTube player and the file viewer are named in the address

The player names what it plays in its own history entry (watch, wrel, wtab): a reload or a
bookmark reopens it on the page that hosts it, with that page's list as the queue, or alone
from the catalog (GET /api/videos/{id}/row); a page that hosts none gets the shell's. Back
lands on the page's address without it (useBackToClose's url; ui/Modal passes it on). The
Files viewer and player do the same (fview, fplay). The Plex and channel-manager views are
always written in full, as their fallback is remembered state.

frontend/src/modules/home/Home.tsx

@@ -78,6 +78,7 @@ import {
   mediaTitleClass,
 } from "../../components/ui/mediaCardStyles";
 import RemoteImage from "../../components/ui/RemoteImage";
+import { useOpenLinkedPlayer } from "../../features/player/useOpenLinkedPlayer";
 
 // The Home surface — "Mit nézzek most?".
 //
@@ -729,6 +730,12 @@ export default function Home() {
     window.history.replaceState({ ...window.history.state, [SAVED_KEY]: question }, "");
   }, [budget, seed, press, seen]);
   const [player, setPlayer] = useState<{ video: Video; startAt: number | null } | null>(null);
+  // A reload or a bookmark of the player reopens it: the video alone, as Home plays it.
+  useOpenLinkedPlayer(
+    true,
+    () => undefined,
+    (video) => setPlayer({ video, startAt: null }),
+  );
 
   // A Plex card's title is in the reader's language, so the answer is cached per language.
   const lang = plexLang(i18n.language);