Fix XSS/loop/webhook findings from Manage Subscriptions review

- Remove member-controlled data (CustomerEmail, subscription Id) from
  onsubmit confirm() JS strings in ManageSubscriptions/Index.cshtml.
  Razor HTML-encoding is decoded by the HTML parser before the JS
  engine sees it, so a literal apostrophe (e.g. o'brien@example.com)
  reached the JS string context, silently skipping confirmation
  (including for irreversible Cancel Now) or enabling stored XSS in
  the admin session. Confirm messages are now static.
- Fix CustomerSubscriptionUpdatedWebHook comparing stripeEvent.Type
  against EventTypes.CustomerUpdated ("customer.updated") instead of
  EventTypes.CustomerSubscriptionUpdated ("customer.subscription.updated"),
  which made the endpoint reject every real event it receives with an
  uncaught 500.
- Harden StripeSubscriptionHandlerService.ListBillableAsync's pagination
  loop against an infinite loop if Stripe ever returns HasMore=true with
  an empty Data page.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: ardalis

src/DevBetterWeb.Infrastructure/SubscriptionHandler/StripeSubscriptionHandler/StripeSubscriptionHandlerService.cs

@@ -35,7 +35,7 @@ public async Task<List<Subscription>> ListBillableAsync(CancellationToken cancel
 			{
 				options.StartingAfter = page.Data[^1].Id;
 			}
-		} while (page.HasMore);
+		} while (page.HasMore && page.Data.Count > 0);
 
 		return subscriptions.Where(s => _billableStatuses.Contains(s.Status)).ToList();
 	}

src/DevBetterWeb.Web/Endpoints/StripeWebhookEndpoints/CustomerSubscriptionUpdatedWebHook.cs

@@ -57,7 +57,7 @@ public override async Task<ActionResult> HandleAsync(CancellationToken cancellat
 
 			_logger.LogInformation($"Processing Stripe Event Type: {stripeEvent.Type}");
 
-			if (stripeEvent.Type != EventTypes.CustomerUpdated)
+			if (stripeEvent.Type != EventTypes.CustomerSubscriptionUpdated)
 			{
 				throw new Exception($"Unhandled Stripe event type {stripeEvent.Type}");
 			}

src/DevBetterWeb.Web/Pages/Admin/ManageSubscriptions/Index.cshtml

@@ -60,21 +60,21 @@
 						else
 						{
 							<form method="post" asp-page-handler="Pause" style="display:inline"
-							      onsubmit="return confirm('Pause collection for @subscription.CustomerEmail? Stripe will stop charging until resumed.');">
+							      onsubmit="return confirm('Pause collection for this customer? Stripe will stop charging until resumed.');">
 								<input type="hidden" name="subscriptionId" value="@subscription.Id" />
 								<button type="submit" class="btn btn-sm btn-warning">Pause</button>
 							</form>
 						}
 						@if (!subscription.CancelAtPeriodEnd)
 						{
 							<form method="post" asp-page-handler="Cancel" style="display:inline"
-							      onsubmit="return confirm('Cancel @subscription.CustomerEmail at period end?');">
+							      onsubmit="return confirm('Cancel this subscription at period end?');">
 								<input type="hidden" name="subscriptionId" value="@subscription.Id" />
 								<button type="submit" class="btn btn-sm btn-outline-danger">Cancel at Period End</button>
 							</form>
 						}
 						<form method="post" asp-page-handler="CancelNow" style="display:inline"
-						      onsubmit="return confirm('IMMEDIATELY cancel @subscription.Id for @subscription.CustomerEmail? This cannot be undone.');">
+						      onsubmit="return confirm('IMMEDIATELY cancel this subscription? This cannot be undone.');">
 							<input type="hidden" name="subscriptionId" value="@subscription.Id" />
 							<button type="submit" class="btn btn-sm btn-danger">Cancel Now</button>
 						</form>