Add metadata language settings for supported APIs

[percefia]

Summary

Adds a global metadata language setting, with optional per-API overrides, so titles, plots, and other localizable fields can be fetched in the user's language when the API supports it.

What changed

• New Languages settings group:
  • Global language
  • per-API overrides: TMDB, Wikipedia, Steam, VNDB, Open Library, MyAnimeList
  • override default is Use global
• APIs that support localization now use that setting:
  • TMDB (movies, series, seasons): language=
  • Wikipedia: chosen language edition
  • Steam: store page language
  • VNDB: preferred title language, fallback to the official title
  • Open Library: search filter by book language (English stays unfiltered)
  • MAL / Tenrai: preferred title (default / English / Japanese)
• OMDb, Comic Vine, BoardGameGeek, RAWG, MusicBrainz, and IGDB are unchanged: they don't expose localizable metadata.
• Unit tests for language mapping and fallbacks.

Test plan

• Default stays English: Wikipedia, Steam, and Open Library behave as before
• Set Global language to French, import a TMDB movie: title/plot/genres come back in French
• Override Wikipedia to Japanese while Global is French: wiki search hits ja.wikipedia.org
• Steam game details follow the Steam override (or the global language)
• VNDB uses the localized title when it exists, otherwise the official title
• Open Library French filters results; English does not add a language filter
• MAL title: Default / English / Japanese, with fallback if a title is missing