fix(plex): the recs rail's anchor and a held recommendation are named in the reader's language (E30 S1b)

Found in the S1b UAT: 'Mert megnézted: Batman Forever' kept the English title, and
the info page's TMDB recommendations kept TMDB's English titles even for titles we
hold. A held recommendation is now named as the library names it, in the reader's
language; one we lack keeps TMDB's title.

backend/tests/test_plex_lang.py

@@ -230,6 +230,25 @@ def _seed_rails(db):
             PlexPlaylistItem(playlist_id=pl.id, item_id=ep.id, position=1),
         ]
     )
+    # TMDB extras: m2 recommends m1 (held) and a title we lack; m1, watched, anchors the recs rail.
+    m1.guid = "tmdb:1"
+    m1.tmdb_enriched_at = datetime(2024, 1, 1, tzinfo=timezone.utc)
+    m1.recommendations = [{"tmdb_id": 2, "title": "EN Only", "media_type": "movie"}]
+    m2 = db.query(PlexItem).filter_by(rating_key="m2").one()
+    m2.guid = "tmdb:2"
+    m2.tmdb_enriched_at = datetime(2024, 1, 1, tzinfo=timezone.utc)
+    m2.recommendations = [
+        {"tmdb_id": 1, "title": "English Title", "media_type": "movie"},
+        {"tmdb_id": 77, "title": "Elsewhere", "media_type": "movie"},
+    ]
+    db.add(
+        PlexState(
+            user_id=user.id,
+            item_id=m1.id,
+            status="watched",
+            watched_at=datetime(2024, 3, 1, tzinfo=timezone.utc),
+        )
+    )
     sysconfig.set_value(db, "plex_enabled", True)
     db.commit()
     return user, pl.id
@@ -259,6 +278,14 @@ def test_every_card_rail_serves_the_readers_language(db, monkeypatch, override_d
         ("Magyar Cím", None),
         ("Kezdet", "Magyar Sorozat"),
     ]
+    # A recommendation we hold is named as the library names it; the rail's anchor too.
+    recs = get("/api/plex/item/m2?lang=hu")["tmdb"]["recommendations"]
+    assert [(r["title"], r["in_library"]) for r in recs] == [
+        ("Magyar Cím", True),
+        ("Elsewhere", False),
+    ]
+    byw = get("/api/plex/discover?scope=both&lang=hu")["because_you_watched"]
+    assert byw["anchor"]["title"] == "Magyar Cím"
     home = get("/api/discover?lang=hu")["continue_watching"]
     plex = [c for c in home if c["source"] == "plex"]
     assert [c["title"] for c in plex] == ["Magyar Sorozat"]