fix(plex): address S6 code-review — 5 findings

1. (correctness) Show hero rating regression: PlexBrowse's show hero rendered a
   rating only when show.imdb_rating was set, so after the S6 IMDb-only change a
   show with no imdb:// entry showed no rating. Now falls back to the audience
   `rating` like PlexInfo.
2. (correctness) ratingMin column mismatch: the rating filter and the /facets
   rating_max now key off coalesce(imdb_rating, rating) — the SAME "best score"
   the badge displays — so a ratingMin picked from a shown IMDb score narrows the
   right column instead of the raw audience `rating`.
3. (altitude) HU search gap: new query.vector_match() matches EITHER vector in HU
   (or_(search_vector_hu, search_vector)) so a row with no HU twin stays findable
   by its English title; ranking still uses the HU vector. field_recheck unions
   the HU+EN per-field tsvectors in HU, staying a strict subset of the prefilter.
4. (test-coverage) Extracted the badge logic to lib/plexRating.pickRatingBadge
   (shared by PlexInfo + the show hero) with a unit test (imdb-preferred, audience
   fallback, 0-score, none). Backend tests added for the HU union search + the
   IMDb-preferred rating filter.
5. (efficiency) Language switch no longer double-fetches the grid: browseQ is
   gated on a committedLang state that lags `lang` by one render, so the
   genre-clear effect settles into a single fetch instead of one throwaway fetch
   with stale-language genres plus a second.

DB-lane suite 295 passed / 2 skip; FE tsc/knip/lint clean, 217 vitest pass.

backend/tests/test_plex_lang.py

@@ -94,3 +94,32 @@ def test_item_detail_language_and_rating_split(db, monkeypatch):
     # 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
+
+
+def test_hu_search_still_finds_en_only_titles(db, monkeypatch):
+    user = _seed(db)
+    # m2 ("EN Only") has no HU twin, so search_vector_hu carries no title tokens for it. HU-mode search
+    # must still match it via the EN vector (vector_match's union) — findable by its English title.
+    resp = _get(db, user, monkeypatch, "/api/plex/library?scope=movie&lang=hu&q=Only")
+    assert "EN Only" in _titles(resp)
+
+
+def test_rating_filter_prefers_imdb_over_audience(db, monkeypatch):
+    lib = PlexLibrary(plex_key="1", title="Movies", kind="movie", enabled=True)
+    db.add(lib)
+    db.flush()
+    # imdb 8.0 but audience 4.0 → a rating_min of 7 must MATCH (filter the displayed best score,
+    # IMDb preferred), where filtering the raw audience column (4.0) would wrongly exclude it.
+    db.add(PlexItem(
+        rating_key="r1", library_id=lib.id, kind="movie", title="High IMDb",
+        imdb_rating=8.0, rating=4.0, year=2001,
+        added_at=datetime(2024, 1, 1, tzinfo=timezone.utc),
+        people_enriched_at=datetime(2024, 1, 1, tzinfo=timezone.utc),
+    ))
+    user = User(email="rating@example.com")
+    db.add(user)
+    db.commit()
+    hit = _get(db, user, monkeypatch, "/api/plex/library?scope=movie&rating_min=7")
+    assert "High IMDb" in _titles(hit)
+    miss = _get(db, user, monkeypatch, "/api/plex/library?scope=movie&rating_min=9")
+    assert "High IMDb" not in _titles(miss)