Fix duplicate WatchProvider rows when the same provider appears twice

Found by running the real test suite against Postgres:
test_ingest_movie_dedupes_watch_provider_across_countries failed with 2
Netflix rows instead of 1 when a movie's watch/providers block lists the
same provider (Netflix, external_id 8) in more than one country -- the
first genuine case in the whole ingestion pipeline where the same
external entity gets resolved via get_or_create twice within one ingest
before anything commits (company/person/collection never have this
shape in existing fixtures).

sync_watch_providers now resolves each distinct provider (by
external_id) at most once per ingest and reuses it for every offering
that references it, rather than calling get_or_create_watch_provider
once per offering regardless of repeats.

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

app/repositories/polymorphic.py

@@ -352,7 +352,17 @@ async def sync_watch_providers(
     distinct WatchProvider touched paired with its current logo_path so the
     caller can sync its logo artwork via company_logo_artwork + sync_artwork
     -- this repository layer doesn't import the services layer to build a
-    NormalizedArtwork itself (see _NormalizedArtworkLike above)."""
+    NormalizedArtwork itself (see _NormalizedArtworkLike above).
+
+    Resolves each distinct provider (by external_id) at most once, even
+    when it appears in several countries/monetization types for the same
+    entity (e.g. Netflix offering both a US and a GB flatrate row) --
+    calling get_or_create_watch_provider a second time for the same
+    external_id later in the same uncommitted session produced a second,
+    duplicate WatchProvider row instead of finding the first (caught
+    against real Postgres; watch providers was the first place in the
+    ingestion pipeline where the same external entity is ever resolved
+    twice within one ingest before anything commits)."""
 
     await session.execute(
         delete(WatchProviderOffering).where(
@@ -361,14 +371,19 @@ async def sync_watch_providers(
         )
     )
     touched: dict[uuid.UUID, tuple[WatchProvider, str | None]] = {}
+    provider_by_external_id: dict[str, WatchProvider] = {}
     for offering in offerings:
         await refs.get_or_create_country(session, offering.country_code, offering.country_code)
+        ext_id = offering.provider.external_id
+        watch_provider = provider_by_external_id.get(ext_id)
+        if watch_provider is None:
             watch_provider = await refs.get_or_create_watch_provider(
                 session,
                 provider_id=tmdb_provider_id,
-            external_id=offering.provider.external_id,
+                external_id=ext_id,
                 name=offering.provider.name,
             )
+            provider_by_external_id[ext_id] = watch_provider
         touched[watch_provider.id] = (watch_provider, offering.provider.logo_path)
         session.add(
             WatchProviderOffering(