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/repositories/collection_repository.py

@@ -4,7 +4,7 @@ from __future__ import annotations
 
 import uuid
 
-from sqlalchemy import select
+from sqlalchemy import func, select
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.models.collection import Collection, CollectionMovie, CollectionSeries
@@ -37,3 +37,24 @@ async def get_collection_series(session: AsyncSession, collection_id: uuid.UUID)
     )
     result = await session.execute(stmt)
     return list(result.scalars().all())
+
+
+async def list_collections(
+    session: AsyncSession, *, limit: int, offset: int
+) -> tuple[list[Collection], int]:
+    """Browse collections -- see movie_repository.list_movies for the
+    window-function total-count approach this mirrors. Collections have no
+    categorical field to filter by and no popularity/date to sort by, so
+    this always orders alphabetically by name (with an id tiebreak for
+    stable pagination)."""
+
+    stmt = (
+        select(Collection, func.count().over().label("total_count"))
+        .order_by(Collection.name.asc(), Collection.id.asc())
+        .limit(limit)
+        .offset(offset)
+    )
+    rows = (await session.execute(stmt)).all()
+    if not rows:
+        return [], 0
+    return [row[0] for row in rows], rows[0].total_count