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]>

docs/api.md

@@ -49,6 +49,7 @@ GET /api/v1/search?q=the%20matrix
 | GET | `/api/v1/movies/{aurora_id}/images` |
 | GET | `/api/v1/movies/{aurora_id}/videos` |
 | GET | `/api/v1/movies/{aurora_id}/recommendations` |
+| GET | `/api/v1/movies/{aurora_id}/watch-providers` |
 | GET | `/api/v1/movies/now-playing` |
 | GET | `/api/v1/movies/upcoming` |
 
@@ -131,6 +132,33 @@ ingested:
 }
 ```
 
+`watch_providers` (embedded on movie/series detail as shown above, or its own
+`GET .../watch-providers`) is grouped by country then by monetization type —
+mirroring TMDb's own `watch/providers` response shape directly, since that's
+the shape a client porting from TMDb already expects:
+
+```json
+{
+  "id": "aur_movie_01m1q7p1c...",
+  "results": {
+    "US": {
+      "link": "https://www.themoviedb.org/movie/603-the-matrix/watch?locale=US",
+      "flatrate": [{ "id": "aur_watch_provider_...", "name": "Netflix", "logo_path": "https://...", "display_priority": 0 }],
+      "rent": [],
+      "buy": [],
+      "ads": [],
+      "free": []
+    }
+  }
+}
+```
+
+**This data comes from JustWatch via TMDb, and carries its own attribution
+requirement separate from TMDb's general one** — TMDb's terms require
+sourcing watch-provider data back to JustWatch specifically if you display
+it, not just crediting TMDb itself. Read TMDb's current terms for the
+exact required wording/logo before showing this in the frontend.
+
 `GET /api/v1/movies/now-playing` and `GET /api/v1/movies/upcoming` use the
 `release_dates` data above rather than `release_date`/`year`: `region`
 (ISO 3166-1 alpha-2, default `US`), `page`, `page_size` — same
@@ -152,6 +180,7 @@ now-playing, soonest for upcoming) rather than appearing twice.
 | GET | `/api/v1/series/{aurora_id}/credits` |
 | GET | `/api/v1/series/{aurora_id}/images` |
 | GET | `/api/v1/series/{aurora_id}/videos` |
+| GET | `/api/v1/series/{aurora_id}/watch-providers` |
 | GET | `/api/v1/seasons/{aurora_id}` |
 | GET | `/api/v1/episodes/{aurora_id}` |