Add watch providers (where to stream/rent/buy)

New TMDb integration end to end: append_to_response "watch/providers",
normalizer parsing grouped by country/monetization type, a WatchProvider
catalog entry (external-id keyed, same get_or_create pattern as Company/
Collection/Person) + polymorphic WatchProviderOffering table (new
migration 0002), ingestion write (including provider logos via the
existing Artwork table), and API exposure -- embedded on movie/series
detail plus a dedicated /watch-providers sub-route, shaped to mirror
TMDb's own response for easy porting.

Note: this data comes from JustWatch via TMDb and carries its own
attribution requirement separate from TMDb's general one -- flagged in
docs/api.md, must be satisfied before showing this in the frontend.

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

app/models/__init__.py

@@ -33,6 +33,7 @@ from app.models.tv import (
     SeriesSpokenLanguage,
 )
 from app.models.video import Video
+from app.models.watch_provider import WatchProvider, WatchProviderOffering
 
 __all__ = [
     "Base",
@@ -72,4 +73,6 @@ __all__ = [
     "Season",
     "Episode",
     "Video",
+    "WatchProvider",
+    "WatchProviderOffering",
 ]