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/PRIVACY.md

@@ -18,6 +18,9 @@ Nothing else leaves your device. There is no telemetry, no crash reporting and n
 of the titles in your library. It does not learn your files, your watch history or your shares.
 Turning them off deletes every stored answer.
 
+**Trailer** on a title's page opens the trailer's YouTube or Dailymotion page in your web
+browser. The app sends nothing there itself; your browser loads the page as it would any link.
+
 ## Secrets
 
 - **The part of a share link after `#`** is the key that decrypts the share. The app treats it as