feat(meta,core,app,android,ios): cast and trailer

AniList's fragment now asks for the first ten characters, main roles
first, with their Japanese voice actor, and for the trailer's site and
id. Both are stored in the existing details JSON as TitleDetails.cast and
.trailer with serde defaults, so no migration is needed and details
stored before them still read. The details REVISION goes to 2, so a
stored match is refetched by its id on the next metadata run and the
cast fills in without anyone matching the title again.

The title page shows a Cast row of round portraits with the character's
name over the actor's. Clicking a tile opens the Person browse page for
that actor, which now also admits voice actors, and search counts them
under People and studios. A Trailer button opens the YouTube or
Dailymotion page in the browser; the app itself makes no request to
either, and an unknown site or an id with odd characters gives no link.

docs/METADATA.md

@@ -162,6 +162,17 @@ match. The same scoring, seeded by the title most recently watched to the end
 and limited to titles not started, is the library's *Because you watched* row.
 No request: it reads only what the match already stored.
 
+**Cast and trailer.** The AniList query also asks for the first ten
+characters by role, main ones first, each with their Japanese voice actor and
+both portraits, and for the trailer's site and id. They are
+`TitleDetails::cast` and `TitleDetails::trailer`, in the same JSON column — no
+migration. `TitleDetails::REVISION` is 2, so a match stored before them is
+fetched again by id on the next match run, as `runtime` was. A voice actor's
+chip opens the same page as a director's (`Facet::Person`). The trailer is
+only ever a link: `Trailer::url` builds the YouTube or Dailymotion address,
+keeping only an id's own characters, and the browser opens it. Portraits are
+fetched like posters, from AniList's image host.
+
 **Android.** The same, through the bridge: `AndroidEngine::arrangement`
 returns the grid's tiles and the shelves as keys into `library`'s titles, and
 each `TitleRecord` carries its display name, franchise and details. The