Add GET /collections browse endpoint; fix embedded collection poster_path

Completes browse/discover across all five entity types: movies, series,
people, companies, and now collections. No filter (no categorical field
like company_type exists for a collection) -- just page/page_size,
always alphabetical by name.

While adding poster_path to CollectionBriefOut for the browse listing,
found the same class of bug fixed earlier for company logo_path:
movie_service's embedded `collection` field never looked up its poster
artwork either, so it stayed null even after ingest_collection populated
one. Fixed alongside since it's the same schema field this feature was
already touching.

Also removed PageMeta from schemas/common.py -- scaffolding from early
spec work that was never actually wired into any endpoint; all five
browse endpoints shipped this session use a flat page/page_size/
total_results/total_pages shape instead.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

app/services/movie_service.py

@@ -54,6 +54,17 @@ async def get_movie_detail(session: AsyncSession, movie_aurora_id: str) -> Movie
 
     cast, crew = split_credits(credits_)
 
+    collection_out: CollectionBriefOut | None = None
+    if movie.collection is not None:
+        collection_posters = await polymorphic.get_artwork(
+            session, "collection", movie.collection.id, ArtworkType.POSTER
+        )
+        collection_out = CollectionBriefOut(
+            id=aurora_id("collection", str(movie.collection.id)),
+            name=movie.collection.name,
+            poster_path=primary_artwork_path(collection_posters, ArtworkType.POSTER),
+        )
+
     company_out: list[CompanyBriefOut] = []
     for company, _role in companies:
         logos = await polymorphic.get_artwork(session, "company", company.id, ArtworkType.LOGO)
@@ -87,13 +98,7 @@ async def get_movie_detail(session: AsyncSession, movie_aurora_id: str) -> Movie
         cast=cast,
         crew=crew,
         companies=company_out,
-        collection=(
-            CollectionBriefOut(
-                id=aurora_id("collection", str(movie.collection.id)), name=movie.collection.name
-            )
-            if movie.collection
-            else None
-        ),
+        collection=collection_out,
         images=to_images_out(artwork),
         videos=[to_video_out(v) for v in videos],
         external_ids=external_ids,