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/services/youtube/oauth_state.rb

@@ -3,8 +3,10 @@ module Youtube
     PURPOSE = :youtube_oauth_connect
 
     class << self
-      def for_team(team_id:, user_id:)
-        verifier.generate([team_id.to_s, user_id.to_s], expires_in: 1.hour)
+      def for_team(team_id:, user_id:, return_app: false)
+        payload = [team_id.to_s, user_id.to_s]
+        payload << "app" if return_app
+        verifier.generate(payload, expires_in: 1.hour)
       end
 
       def for_platform(admin_id:)
@@ -17,8 +19,13 @@ module Youtube
         when Array
           if payload.first == "platform"
             { kind: :platform, admin_id: payload[1] }
-          elsif payload.size == 2
-            { kind: :team, team_id: payload[0], user_id: payload[1] }
+          elsif payload.size >= 2
+            {
+              kind: :team,
+              team_id: payload[0],
+              user_id: payload[1],
+              return_app: payload[2] == "app"
+            }
           else
             raise ArgumentError, "stato OAuth non valido"
           end