fix: add back TvDB IDs for series links in APIv2

- Added back the TvDB IDs for the series links endpoint in APIv2 because Shoko Metadata may be using them for theme videos. But this time it's sourced from the TMDB data, since the TvDB data is gone.

Shoko.Server/API/v2/Modules/Common.cs

@@ -3239,7 +3239,11 @@ public static Dictionary<string, object> GetLinks(int id)
 
         var serie = RepoFactory.AnimeSeries.GetByID(id);
         var trakt = serie?.TraktShow;
-        if (trakt != null) links.Add("trakt", trakt.Where(a => !string.IsNullOrEmpty(a.URL)).Select(x => x.URL).ToArray());
+        if (trakt != null)
+            links.Add("trakt", trakt.Where(a => !string.IsNullOrEmpty(a.URL)).Select(x => x.URL).ToArray());
+
+        if (serie?.TmdbShows is { Count: > 0 } tmdbShows)
+            links.Add("tvdb", tmdbShows.Select(x => x.TvdbShowID).WhereNotNull().ToArray());
 
         if (serie?.TmdbMovieCrossReferences is { Count: > 0 } tmdbMovieXrefs)
             links.Add("tmdb", tmdbMovieXrefs[0].TmdbMovieID);