Billing upgrade/downgrade, inviti in app e diretta YouTube da mobile.

Upgrade Stripe con addebito immediato; downgrade programmato a fine periodo.
UX billing più sobria con box info; icone piani. API inviti e OAuth YouTube
per staff trasmissione; deep link join; scelta partita programmata o nuova.

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

backend/app/controllers/api/v1/teams_controller.rb

@@ -103,7 +103,8 @@ module Api
           youtube_enabled: ent.youtube_enabled?,
           youtube_mode: ent.plan.youtube_mode,
           staff_role: current_user.staff_role_for(team),
-          can_stream: current_user.can_stream_for?(team)
+          can_stream: current_user.can_stream_for?(team),
+          can_connect_youtube: current_user.can_stream_for?(team) && ent.premium_full? && ent.youtube_enabled?
         }
         if detail
           data[:members] = team.user_teams.includes(:user).where.not(role: "owner").map do |ut|