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/spec/services/billing/stripe/plan_change_kind_spec.rb

@@ -0,0 +1,32 @@
+require "rails_helper"
+
+RSpec.describe Billing::Stripe::PlanChangeKind do
+  before { load Rails.root.join("db/seeds/plans.rb") }
+
+  it "classifica light → full come upgrade" do
+    expect(described_class.classify(
+      from_plan_slug: "premium_light",
+      from_interval: "monthly",
+      to_plan_slug: "premium_full",
+      to_interval: "monthly"
+    )).to eq(:upgrade)
+  end
+
+  it "classifica full → light come downgrade" do
+    expect(described_class.classify(
+      from_plan_slug: "premium_full",
+      from_interval: "monthly",
+      to_plan_slug: "premium_light",
+      to_interval: "monthly"
+    )).to eq(:downgrade)
+  end
+
+  it "classifica passaggio a annuale come upgrade sullo stesso piano" do
+    expect(described_class.classify(
+      from_plan_slug: "premium_light",
+      from_interval: "monthly",
+      to_plan_slug: "premium_light",
+      to_interval: "yearly"
+    )).to eq(:upgrade)
+  end
+end