fix(plugin-ecommerce): verify PaymentIntent succeeded before creating…

[nehaaprasad]

what?

Prevents stripe/confirm-order from creating an order unless the Stripe PaymentIntent is actually successful.

Why?

• Failed or canceled payments could still create an order, mark the cart as purchased, and set the transaction to succeeded.

How?

• After retrieving the PaymentIntent, check paymentIntent.status === 'succeeded'.
  If not, throw an error and stop before any order/cart/transaction updates.

Fixes #15862