feat(plex): S6 backend — language-aware serving + IMDb-only rating

E5 S6 backend half (no migration — the *_hu / rich columns exist from S5a/S5b).

Language-aware serving (?lang=hu serves the HU overlay twin, EN fallback per row):
- query.py: column pickers title_col / genres_col / vector_col; field_recheck and
  meta_filter_conds take `lang`. DISPLAY/FILTER pickers coalesce(*_hu, *) (EN
  fallback); SEARCH pickers use the raw *_hu column mirroring the generated
  search_vector_hu (coalesce to '', not EN) so the field recheck stays a strict
  subset of the GIN vector (the S2 invariant). genres_col type_coerces the coalesce
  to JSONB so the GIN `.contains` survives.
- browse.py: `lang` param on /library, /facets, /item, /show (validated to en|hu).
  unified_library title/vector/rank/field-scope + meta filters are language-aware
  for both the movie and show branches; facets unnest the active-language genre
  vocabulary (jsonb_typeof guard kept); detail endpoints serve HU title/summary/
  genres/show_title with EN fallback. Episodes stay EN (not overlay-localized).

IMDb-only rating (folded-in S5b review #5):
- detail.py rich_detail: drop the audienceRating/rating fallback → imdb_rating is
  NULL when there's no imdb:// Rating entry (stop mislabelling a Plex audience score
  as IMDb). item_detail now also serves the `rating` column (audience score;
  show_detail already did) so the UI can show it when there's no IMDb score.

Tests: test_plex_lang.py (HU title serving + EN fallback, language-specific facet
vocabulary, genre-filter language matching, item_detail lang + rating split);
test_plex_detail updated for IMDb-only. DB-lane suite 293 passed / 2 skipped; ruff clean.

backend/tests/test_plex_detail.py

@@ -57,9 +57,11 @@ def test_rich_detail_prefers_imdb_entry_and_builds_link():
     assert d["cast"][1]["thumb"] is None  # no CDN headshot → not proxied
 
 
-def test_rich_detail_falls_back_to_audience_rating():
+def test_rich_detail_is_imdb_only_no_audience_fallback():
+    # E5 S6: imdb_rating is IMDb-ONLY. With no imdb:// Rating entry it's NULL — the Plex audience score
+    # is NOT mislabelled as an IMDb score (it's served separately via the `rating` column).
     d = detail.rich_detail({"audienceRating": 7.25})
-    assert d["imdb_rating"] == 7.2  # rounded to 1dp
+    assert d["imdb_rating"] is None
     assert d["imdb_id"] is None and d["imdb_url"] is None
 
 

backend/tests/test_plex_lang.py

@@ -0,0 +1,96 @@
+"""E5 S6: HU-overlay language serving. When ?lang=hu, the unified library, facets, genre filter and
+detail endpoints serve the Hungarian `*_hu` columns (falling back to EN where a row has no HU twin);
+?lang=en (the default) serves English. Also covers the imdb_rating IMDb-only / audience-score split.
+DB lane (`db` fixture) — skipped without Postgres.
+"""
+from datetime import datetime, timezone
+
+from fastapi.testclient import TestClient
+
+import app.state as state
+from app.auth import current_user
+from app.db import get_db
+from app.main import app
+from app.models import PlexItem, PlexLibrary, User
+
+
+def _seed(db):
+    """One EN movie library with a single movie that has both EN and HU metadata, plus a second movie
+    that is EN-only (no HU twin) to prove the coalesce fallback."""
+    lib = PlexLibrary(plex_key="1", title="Movies", kind="movie", enabled=True)
+    db.add(lib)
+    db.flush()
+    m1 = PlexItem(
+        rating_key="m1", library_id=lib.id, kind="movie",
+        title="English Title", title_hu="Magyar Cím",
+        summary="English summary.", summary_hu="Magyar összefoglaló.",
+        genres=["Drama"], genres_hu=["Dráma"],
+        rating=6.5, imdb_rating=None,
+        year=2001, added_at=datetime(2024, 1, 1, tzinfo=timezone.utc),
+        people_enriched_at=datetime(2024, 1, 1, tzinfo=timezone.utc),  # serve from row, skip live enrich
+    )
+    m2 = PlexItem(
+        rating_key="m2", library_id=lib.id, kind="movie",
+        title="EN Only", genres=["Comedy"],  # no HU twin
+        year=2002, added_at=datetime(2024, 1, 2, tzinfo=timezone.utc),
+        people_enriched_at=datetime(2024, 1, 2, tzinfo=timezone.utc),
+    )
+    db.add_all([m1, m2])
+    user = User(email="plexlang@example.com")
+    db.add(user)
+    db.commit()
+    return user
+
+
+def _get(db, user, monkeypatch, path):
+    monkeypatch.setattr(state, "_configured_cache", True)  # the request gate 503s an unconfigured app
+    app.dependency_overrides[get_db] = lambda: db
+    app.dependency_overrides[current_user] = lambda: user
+    try:
+        client = TestClient(app)  # no context manager: skip lifespan
+        return client.get(path)
+    finally:
+        app.dependency_overrides.clear()
+
+
+def _titles(resp):
+    return {i["title"] for i in resp.json()["items"]}
+
+
+def test_library_serves_active_language_titles(db, monkeypatch):
+    user = _seed(db)
+    hu = _get(db, user, monkeypatch, "/api/plex/library?scope=movie&lang=hu")
+    en = _get(db, user, monkeypatch, "/api/plex/library?scope=movie&lang=en")
+    # HU serves the twin's Hungarian title; the EN-only row falls back to its English title.
+    assert _titles(hu) == {"Magyar Cím", "EN Only"}
+    assert _titles(en) == {"English Title", "EN Only"}
+
+
+def test_facets_vocabulary_is_language_specific(db, monkeypatch):
+    user = _seed(db)
+    hu = _get(db, user, monkeypatch, "/api/plex/facets?scope=movie&lang=hu")
+    en = _get(db, user, monkeypatch, "/api/plex/facets?scope=movie&lang=en")
+    hu_genres = {g["value"] for g in hu.json()["genres"]}
+    en_genres = {g["value"] for g in en.json()["genres"]}
+    assert "Dráma" in hu_genres and "Drama" not in hu_genres
+    assert "Drama" in en_genres and "Dráma" not in en_genres
+
+
+def test_genre_filter_matches_active_language_vocabulary(db, monkeypatch):
+    user = _seed(db)
+    # The HU genre chip filters the HU column; the same string against the EN column matches nothing.
+    hit = _get(db, user, monkeypatch, "/api/plex/library?scope=movie&lang=hu&genres=Dráma")
+    miss = _get(db, user, monkeypatch, "/api/plex/library?scope=movie&lang=en&genres=Dráma")
+    assert _titles(hit) == {"Magyar Cím"}
+    assert miss.json()["items"] == []
+
+
+def test_item_detail_language_and_rating_split(db, monkeypatch):
+    user = _seed(db)
+    resp = _get(db, user, monkeypatch, "/api/plex/item/m1?lang=hu")
+    body = resp.json()
+    assert body["title"] == "Magyar Cím"
+    assert body["summary"] == "Magyar összefoglaló."
+    # imdb_rating is IMDb-only (None here); the audience score is served separately as `rating`.
+    assert body["imdb_rating"] is None
+    assert body["rating"] == 6.5