Add keyword browsing/filtering and expose alternate titles

Keywords were ingested and shown read-only on detail pages, but had no
directory (GET /keywords) or filter param -- the same gap genres had
before today. Mirrors the genre browse pattern exactly: repository,
service, route, plus a `keyword` filter on GET /movies and GET /series.

Alternate/translated titles ("Also Known As") were normalized down to
bare title strings and never written to MovieAlternateTitle/
SeriesAlternateTitle at all. Normalizer now captures country_code + type
per TMDb's actual shape; ingestion writes them; movie/series detail now
expose an alternate_titles list.

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

app/services/common.py

@@ -6,9 +6,11 @@ from app.core.ids import aurora_id
 from app.models.artwork import Artwork
 from app.models.credit import Credit
 from app.models.enums import ArtworkType
-from app.models.movie import ReleaseDate
+from app.models.movie import MovieAlternateTitle, ReleaseDate
+from app.models.tv import SeriesAlternateTitle
 from app.models.video import Video
 from app.schemas.common import (
+    AlternateTitleOut,
     ArtworkOut,
     CastCreditOut,
     CertificationOut,
@@ -73,6 +75,10 @@ def to_video_out(video: Video) -> VideoOut:
     )
 
 
+def to_alternate_title_out(alt: MovieAlternateTitle | SeriesAlternateTitle) -> AlternateTitleOut:
+    return AlternateTitleOut(title=alt.title, country_code=alt.country_code, type=alt.type)
+
+
 def to_release_date_out(release_date: ReleaseDate) -> ReleaseDateOut:
     certification = None
     if release_date.certification is not None: