fix(plex): show-library collections get montage art too (A3)

The collection browse-tile montage queried only movie members, so show-library
collections (IMDb Popular, TMDb Trending, … in the TV library) rendered as bare colour
tiles. Union the art from PlexShow members as well (a collection lives in one library, so
exactly one side has art); fall back to the collection's own poster, then the colour hash.
Runtime stays movie-only (shows have no single duration).

Verified live: every collection now shows a montage (0 art-less tiles, was ~all the show
collections).

Gate: backend ruff clean, 5 collections tests (+ a show-collection art assertion).

backend/app/routes/plex/collections.py

@@ -11,6 +11,7 @@ from app.models import (
     PlexCollection,
     PlexItem,
     PlexLibrary,
+    PlexShow,
     User,
 )
 from app.plex import sync as plex_sync
@@ -95,17 +96,25 @@ def collections(
             func.lower(PlexCollection.title),
         )
     ).scalars().all()
-    # A montage of the top films per tile + the collection's total runtime (color hash + no-runtime is
-    # the client fallback for show-only / empty collections). Two grouped queries over the movie libs.
-    movie_ids, _show_ids = _content_libs(db)
+    # A montage of the top titles per tile + the collection's total runtime. Art unions MOVIE and SHOW
+    # members (a collection lives in one library, so exactly one side has art) — a show collection would
+    # otherwise render blank; the collection's own poster is the next fallback, then the colour hash.
+    # Runtime is movie-only (shows have no single duration).
+    movie_ids, show_ids = _content_libs(db)
     keys = [c.rating_key for c in rows]
-    art = top_art_keys(db, PlexItem, movie_ids, PlexItem.collection_keys, keys, per=2)
+    art_m = top_art_keys(db, PlexItem, movie_ids, PlexItem.collection_keys, keys, per=2)
+    art_s = top_art_keys(db, PlexShow, show_ids, PlexShow.collection_keys, keys, per=2)
     runtime = runtime_by_key(db, PlexItem, movie_ids, PlexItem.collection_keys, keys)
+
+    def _art(c: PlexCollection) -> list[str]:
+        member = art_m.get(c.rating_key) or art_s.get(c.rating_key)
+        return member or ([c.rating_key] if c.thumb_key else [])
+
     return {
         "collections": [
             {
                 **_collection_card(c),
-                "art": art.get(c.rating_key, []),
+                "art": _art(c),
                 "total_runtime_s": runtime.get(c.rating_key, 0),
             }
             for c in rows

backend/tests/test_plex_collections_filter.py

@@ -10,7 +10,7 @@ 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 PlexCollection, PlexItem, PlexLibrary, User
+from app.models import PlexCollection, PlexItem, PlexLibrary, PlexShow, User
 
 
 def _seed(db):
@@ -92,3 +92,25 @@ def test_collection_cards_carry_montage_art_and_total_runtime(db, monkeypatch):
                 if c["id"] == "A")
     assert card["art"] == ["m2", "m1"]  # best-rated first (m2 9.0 > m1 8.0)
     assert card["total_runtime_s"] == 5400  # 3600 + 1800
+
+
+def test_show_collection_gets_montage_art_from_shows(db, monkeypatch):
+    # A show-library collection must get its montage from PlexShow members (else it renders blank) — the
+    # A3 fix that unions movie + show art. Runtime stays 0 (shows have no single duration).
+    lib = PlexLibrary(plex_key="2", title="Shows", kind="show", enabled=True)
+    db.add(lib)
+    db.flush()
+    db.add(PlexCollection(rating_key="S", library_id=lib.id, title="Show Coll", child_count=2))
+    db.add_all([
+        PlexShow(rating_key="s1", library_id=lib.id, title="S1", collection_keys=["S"], rating=7.0,
+                 added_at=datetime(2024, 1, 1, tzinfo=timezone.utc)),
+        PlexShow(rating_key="s2", library_id=lib.id, title="S2", collection_keys=["S"], rating=9.0,
+                 added_at=datetime(2024, 1, 2, tzinfo=timezone.utc)),
+    ])
+    user = User(email="showcoll@example.com")
+    db.add(user)
+    db.commit()
+    card = next(c for c in _get(db, user, monkeypatch, "/api/plex/collections").json()["collections"]
+                if c["id"] == "S")
+    assert card["art"] == ["s2", "s1"]  # show members, best-rated first
+    assert card["total_runtime_s"] == 0