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.

web/src/series.ts

@@ -2,7 +2,7 @@
 // release schemas — same reasoning as search.ts: the generated client
 // (src/api/) is uncommitted, so CI's tsc cannot see it.
 
-import type { MetadataCastMember, MetadataTrailer } from "./movie";
+import type { MetadataTrailer } from "./movie";
 import type { ActionOutcome, MovieRelease, ReleasesOutcome, WaiveOutcome } from "./releases";
 import { errorDetail, probedAttributeTags, waiverOverride } from "./releases";
 
@@ -259,7 +259,6 @@ export interface SeriesMetadata {
   homepage: string | null;
   /** §9.6 links out to TVDB for series; absent when the id is unknown. */
   tvdb_id: number | null;
-  cast: MetadataCastMember[];
   trailer: MetadataTrailer | null;
 }