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/invitations_controller.rb

@@ -0,0 +1,52 @@
+module Api
+  module V1
+    class InvitationsController < BaseController
+      skip_before_action :authenticate_request!, only: :show
+
+      def show
+        invitation = find_pending_invitation
+        unless invitation
+          return render json: { valid: false, error: "Invito non valido o scaduto" }, status: :not_found
+        end
+
+        render json: {
+          valid: true,
+          email: invitation.email,
+          team_id: invitation.team_id,
+          team_name: invitation.team.name,
+          club_name: invitation.team.club.name,
+          staff_kind: invitation.staff_kind,
+          expires_at: invitation.expires_at
+        }
+      end
+
+      def accept
+        invitation = find_pending_invitation
+        return render json: { error: "Invito non valido o scaduto" }, status: :not_found unless invitation
+
+        if current_user.email.downcase != invitation.email.downcase
+          return render json: {
+            error: "Questo invito è per #{invitation.email}. Accedi con quell'indirizzo email.",
+            invited_email: invitation.email
+          }, status: :unprocessable_entity
+        end
+
+        invitation.accept!(current_user)
+        render json: {
+          team_id: invitation.team_id,
+          team_name: invitation.team.name,
+          message: "Sei entrato in #{invitation.team.name} come responsabile trasmissione."
+        }
+      end
+
+      private
+
+      def find_pending_invitation
+        token = params[:token].to_s
+        return nil if token.blank?
+
+        TeamInvitation.pending.find_by(token_digest: Digest::SHA256.hexdigest(token))
+      end
+    end
+  end
+end