refactor(web): drop cast from title detail

DESIGN.md §9.6 no longer carries cast (#163). Removes the cast
sections, the MetadataCastMember schema and field from both metadata
responses, and every .cast-* rule. arr-meta keeps CastMember and the
credits append; the TMDB call is unchanged.

crates/arr-api/src/lib.rs

@@ -25,7 +25,7 @@ use utoipa_axum::routes;
 use utoipa_scalar::{Scalar, Servable};
 
 pub use health::{Check, Health, HealthReport, Status};
-pub use metadata::{MetadataCastMember, MetadataTrailer, MovieMetadata, SeriesMetadata};
+pub use metadata::{MetadataTrailer, MovieMetadata, SeriesMetadata};
 pub use movies::{
     Accepted, AttentionQueues, CreateMovie, ErrorBody, Movie, MovieFile, Release, UpdateMovie,
 };