docs(site): move I18nProvider to Components sidebar section

Group I18nProvider with Player.Provider and Player.Container as
infrastructure providers; keep createI18n and hooks under Hooks & Utilities.

Co-authored-by: Cursor <cursoragent@cursor.com>

site/src/docs.config.ts

@@ -66,6 +66,7 @@ export const sidebar: Sidebar = [
     contents: [
       { slug: 'reference/player-provider' },
       { slug: 'reference/player-container' },
+      { slug: 'reference/i18n-provider' },
       // sorted alphabetically
       { slug: 'reference/airplay-button' },
       { slug: 'reference/audio-track-radio-group' },