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/api/v1/collections.py

@@ -2,13 +2,13 @@
 
 from __future__ import annotations
 
-from fastapi import APIRouter, Depends
+from fastapi import APIRouter, Depends, Query
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.api.deps import not_found
 from app.core.database import get_db
 from app.core.security import enforce_rate_limit
-from app.schemas.collection import CollectionDetailOut
+from app.schemas.collection import CollectionDetailOut, CollectionListOut
 from app.services import collection_service
 
 router = APIRouter(
@@ -16,6 +16,15 @@ router = APIRouter(
 )
 
 
+@router.get("", response_model=CollectionListOut)
+async def list_collections(
+    page: int = Query(1, ge=1),
+    page_size: int = Query(20, ge=1, le=50),
+    session: AsyncSession = Depends(get_db),
+) -> CollectionListOut:
+    return await collection_service.list_collections(session, page=page, page_size=page_size)
+
+
 @router.get("/{aurora_id}", response_model=CollectionDetailOut)
 async def get_collection(
     aurora_id: str, session: AsyncSession = Depends(get_db)