fix: Show cancellation message when subscription is pending cancellation (#752)

* fix: Show cancellation message when subscription is pending cancellation

When a subscription is cancelled via Stripe, the UI incorrectly showed
"Your contribution continues on..." instead of reflecting the cancellation
status. This fix adds tracking of `cancel_at_period_end` from Stripe webhooks
and displays "Your contribution ends on..." when a subscription has been
cancelled but is still active until the billing period ends.

https://claude.ai/code/session_01Y8ELTdK1k9o315iSq43TRN

* chore: Update schema.rb with cancel_at_period_end column

https://claude.ai/code/session_01Y8ELTdK1k9o315iSq43TRN

* Schema version

---------

Co-authored-by: Claude <noreply@anthropic.com>

test/models/provider/stripe/subscription_event_processor_test.rb

@@ -13,6 +13,7 @@ class Provider::Stripe::SubscriptionEventProcessorTest < ActiveSupport::TestCase
           id: test_subscription_id,
           status: "active",
           customer: test_customer_id,
+          cancel_at_period_end: false,
           items: {
             data: [
               {
@@ -53,5 +54,52 @@ class Provider::Stripe::SubscriptionEventProcessorTest < ActiveSupport::TestCase
     assert_equal 9, family.subscription.amount
     assert_equal "USD", family.subscription.currency
     assert family.subscription.current_period_ends_at > 20.days.from_now
+    assert_equal false, family.subscription.cancel_at_period_end
+  end
+
+  test "handles subscription cancellation at period end" do
+    test_customer_id = "test-customer-id-cancel"
+    test_subscription_id = "test-subscription-id-cancel"
+
+    mock_event = JSON.parse({
+      type: "customer.subscription.updated",
+      data: {
+        object: {
+          id: test_subscription_id,
+          status: "active",
+          customer: test_customer_id,
+          cancel_at_period_end: true,
+          items: {
+            data: [
+              {
+                current_period_end: 1.month.from_now.to_i,
+                plan: {
+                  interval: "month",
+                  amount: 900,
+                  currency: "usd"
+                }
+              }
+            ]
+          }
+        }
+      }
+    }.to_json, object_class: OpenStruct)
+
+    family = Family.create!(
+      name: "Test Cancelling Family",
+      stripe_customer_id: test_customer_id
+    )
+
+    family.start_subscription!(test_subscription_id)
+
+    processor = Provider::Stripe::SubscriptionEventProcessor.new(mock_event)
+    processor.process
+
+    family.reload
+
+    assert_equal "active", family.subscription.status
+    assert_equal true, family.subscription.cancel_at_period_end
+    assert family.subscription.pending_cancellation?
+    assert family.subscription_pending_cancellation?
   end
 end