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/common.py

@@ -112,6 +112,19 @@ class CollectionBriefOut(BaseModel):
     poster_path: str | None = None
 
 
+class CertificationOut(BaseModel):
+    system: str
+    rating: str
+
+
+class ReleaseDateOut(BaseModel):
+    country_code: str
+    release_date: date
+    release_type: str | None = None
+    certification: CertificationOut | None = None
+    note: str | None = None
+
+
 class ErrorDetail(BaseModel):
     code: str
     message: str