fix(plex): an episode with no number is named by its title on every card

The cards, the up-next card and the mark-next label printed a question
mark where Plex has no number; the player's header already showed the
title alone. One helper (episodeNumbers/episodeName) for every place.

frontend/src/components/UpNextCard.tsx

@@ -6,6 +6,7 @@ import { api } from "../lib/api";
 import { plexLang } from "../i18n";
 import { qk } from "../lib/queryKeys";
 import { cardImage } from "../lib/plexImage";
+import { episodeNumbers } from "../lib/plexDetail";
 import { Button } from "./ui/Button";
 import { IconButton } from "./ui/IconButton";
 
@@ -55,10 +56,14 @@ export function UpNextCard({
   const R = 10;
   const C = 2 * Math.PI * R;
 
-  // Title: "Show · S2·E5" over the episode title for episodes; the plain title for movies/queue items.
+  // Title: "Show · S2·E5" over the episode title for episodes (the show alone when Plex has no
+  // number for the episode); the plain title for movies/queue items.
+  const nums = next ? episodeNumbers(next) : null;
   const heading =
     next?.kind === "episode" && next.show_title
-      ? `${next.show_title} · S${next.season_number ?? "?"}·E${next.episode_number ?? "?"}`
+      ? nums
+        ? `${next.show_title} · S${nums.season}·E${nums.episode}`
+        : next.show_title
       : (next?.title ?? "");
   const sub = next?.kind === "episode" ? next.title : null;