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/providers/tmdb.py

@@ -27,8 +27,14 @@ from app.providers.base import (
     ProviderRateLimitedError,
 )
 
-_MOVIE_APPEND = "credits,images,videos,keywords,alternative_titles,external_ids,release_dates,recommendations"
-_SERIES_APPEND = "credits,images,videos,keywords,alternative_titles,external_ids,content_ratings"
+_MOVIE_APPEND = (
+    "credits,images,videos,keywords,alternative_titles,external_ids,release_dates,"
+    "recommendations,watch/providers"
+)
+_SERIES_APPEND = (
+    "credits,images,videos,keywords,alternative_titles,external_ids,content_ratings,"
+    "watch/providers"
+)
 _PERSON_APPEND = "external_ids,images,combined_credits"
 
 _DEFAULT_EXPONENTIAL_WAIT = wait_exponential(multiplier=0.5, max=5)