Add GET /movies and GET /series browse/discover endpoints

The complement to /search for browsing without a query: paginated,
filterable (genre, year, status) and sortable (popularity,
release/air date, rating, title) listings. Offset-based pagination
rather than the Aurora ID cursor scheme, since sorting by
popularity/rating/date doesn't line up with creation-order cursors.

Total count is computed via a window function in the same query as
the page of results, avoiding a second round trip per request. An
invalid filter (malformed genre id, unknown status) is a 422 via a
per-service InvalidMovieFilterError/InvalidSeriesFilterError, caught
before any DB query runs.

build_movie_summary/build_series_summary refactored to share their
row-to-summary logic with the new list path, avoiding a redundant
get_by_id lookup when the row is already in hand.

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

app/schemas/movie.py

@@ -83,3 +83,11 @@ class MovieVideosOut(BaseModel):
 class MovieRecommendationsOut(BaseModel):
     id: str
     recommendations: list[MovieSummaryOut] = []
+
+
+class MovieListOut(BaseModel):
+    page: int
+    page_size: int
+    total_results: int
+    total_pages: int
+    results: list[MovieSummaryOut] = []