Expose certifications and per-country release dates

TMDb's release_dates/content_ratings blocks were already fetched via
append_to_response but discarded at normalization -- every downstream
layer (ingestion write, repository read, schema, service) was unbuilt.
Adds the full pipeline: NormalizedReleaseDate + get_or_create_certification,
a shared polymorphic sync/read (movie and series both use it), and
MovieDetailOut/SeriesDetailOut certification + release_dates fields.

Series content_ratings has no date of its own, so each rating is anchored
to the show's first_air_date with release_type="tv".

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

app/schemas/movie.py

@@ -14,6 +14,7 @@ from app.schemas.common import (
     GenreOut,
     ImagesOut,
     KeywordOut,
+    ReleaseDateOut,
     VideoOut,
 )
 
@@ -49,6 +50,10 @@ class MovieDetailOut(BaseModel):
     vote_average: float | None = None
     vote_count: int | None = None
     adult: bool = False
+    # The US MPA rating (e.g. "PG-13"), the badge TMDb shows next to a
+    # title by default -- convenience pick out of `release_dates` below for
+    # a client that just wants a single rating without picking a country.
+    certification: str | None = None
 
     genres: list[GenreOut] = []
     keywords: list[KeywordOut] = []
@@ -58,6 +63,7 @@ class MovieDetailOut(BaseModel):
     collection: CollectionBriefOut | None = None
     images: ImagesOut = ImagesOut()
     videos: list[VideoOut] = []
+    release_dates: list[ReleaseDateOut] = []
     external_ids: dict[str, str] = {}
 
     created_at: datetime