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/tests/test_plex_person_bio.py

@@ -332,3 +332,74 @@ def test_person_detail_serves_bio_and_resolves_known_for(db, monkeypatch, overri
     assert j["also_known_as"] == ["Alt Name"]
     # Only the in-library known_for credit resolves to a card; the out-of-library one is dropped.
     assert [c["title"] for c in j["known_for"]] == ["Known Movie"]
+
+
+# --- E30 S4: the biography in the reader's language --------------------------------------------------
+# The same /person request appends `translations`; the Hungarian one is kept beside the instance-language
+# biography, and a Hungarian reader is served it, falling back to the English one when TMDB has none.
+
+
+def _translation(lang: str, bio: str) -> dict:
+    return {"iso_639_1": lang, "iso_3166_1": lang.upper(), "data": {"biography": bio}}
+
+
+def test_parse_person_keeps_the_hungarian_biography():
+    payload = {
+        **PAYLOAD,
+        "translations": {
+            "translations": [
+                _translation("de", "Ein Schauspieler."),
+                _translation("hu", "  Ünnepelt színész.  "),
+            ]
+        },
+    }
+    assert plex_tmdb.parse_person(payload)["biography_hu"] == "Ünnepelt színész."
+
+
+def test_parse_person_without_a_hungarian_biography():
+    assert plex_tmdb.parse_person(PAYLOAD)["biography_hu"] is None
+    blank = {**PAYLOAD, "translations": {"translations": [_translation("hu", "   ")]}}
+    assert plex_tmdb.parse_person(blank)["biography_hu"] is None
+
+
+def test_fetch_person_asks_for_the_translations():
+    client = plex_tmdb.TmdbClient.__new__(plex_tmdb.TmdbClient)
+    seen: list[dict] = []
+    client._get = lambda path, params=None: seen.append(params or {}) or {}  # type: ignore[method-assign]
+    client.fetch_person(500)
+    assert "translations" in seen[0]["append_to_response"].split(",")
+
+
+def test_person_detail_serves_the_biography_in_the_readers_language(db, monkeypatch, override_dep):
+    from datetime import datetime, timezone
+
+    done = datetime(2024, 1, 1, tzinfo=timezone.utc)
+    db.add(PlexLibrary(plex_key="7", title="Movies", kind="movie", enabled=True))
+    db.add_all(
+        [
+            PlexPerson(
+                name="Both P",
+                tmdb_person_id=1,
+                tmdb_enriched_at=done,
+                biography="English bio.",
+                biography_hu="Magyar életrajz.",
+            ),
+            PlexPerson(
+                name="Only EN P", tmdb_person_id=2, tmdb_enriched_at=done, biography="Only English."
+            ),
+        ]
+    )
+    user = User(email="biolang@example.com")
+    db.add(user)
+    db.commit()
+
+    def bio(name: str, lang: str) -> str | None:
+        resp = _get(db, user, monkeypatch, override_dep, f"/api/plex/person/{name}?lang={lang}")
+        assert resp.status_code == 200, resp.text
+        return resp.json()["biography"]
+
+    assert bio("Both P", "hu") == "Magyar életrajz."
+    assert bio("Both P", "en") == "English bio."
+    assert (
+        bio("Only EN P", "hu") == "Only English."
+    )  # TMDB has no Hungarian one: the English stands in