fix(plex): an episode Plex has no number for is named by its title alone

The OS media title printed the missing number as "Enull", the player and info headers as a bare
"E". One helper for the three lines.

frontend/src/components/PlexInfo.tsx

@@ -10,6 +10,7 @@ import { DetailCustomizeMenu, Filterable, PrefToggle } from "./plexDetailUi";
 import { DetailAside, DetailAsideToggles, DetailKeywords } from "./plexDetailAside";
 import {
   DETAIL_POSTER,
+  episodeLine,
   tmdbBackdropUrl,
   useCrossfadeBackdrop,
   useDetailAside,
@@ -315,7 +316,7 @@ export default function PlexInfo({
               )}
               {detail.kind === "episode" && (
                 <p className={`text-sm ${overlay ? "text-white/70" : "text-muted"}`}>
-                  S{detail.season_number}·E{detail.episode_number} — {detail.title}
+                  {episodeLine(detail)}
                 </p>
               )}
             </div>