feat(i18n): the person page's biography in Hungarian, from TMDB's translation (E30 S4)

The /person fetch appends translations and keeps TMDB's Hungarian biography beside the instance-language
one (new plex_people.biography_hu, migration 0092). A Hungarian reader is served it, the English one when
TMDB has none. Already-enriched people are un-stamped, so their next open refetches them once.

backend/app/routes/plex/people.py

@@ -243,7 +243,10 @@ def person_detail(
     return {
         "name": name,
         "photo": person.photo_thumb if person else None,
-        "biography": person.biography if person else None,
+        # The Hungarian biography for a Hungarian reader, the instance-language one when TMDB has none.
+        "biography": ((person.biography_hu if lang == "hu" else None) or person.biography)
+        if person
+        else None,
         "birthday": person.birthday if person else None,
         "deathday": person.deathday if person else None,
         "place_of_birth": person.place_of_birth if person else None,