fix(payments-next): use pending_setup_intent

[StaberindeZA]

Because

• Checkout for zero invoice amount currently always creates and confirms a new setup intent, instead of using the pending setup intent on the subscription.

This pull request

• When available, confirm the pending setup intent on the newly created subscription.

Issue that this pull request solves

Closes: (issue number)

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[Copilot]

Pull request overview

This PR updates the Stripe checkout flow for zero-amount invoices so that, when a newly created subscription includes a pending_setup_intent, the system confirms that existing setup intent instead of always creating and confirming a new one. This aligns the checkout behavior with Stripe’s subscription state and avoids redundant setup intent creation.

Changes:

• Add StripeClient.setupIntentConfirm() and expose it via SetupIntentManager.confirm().
• Update CheckoutService to confirm subscription.pending_setup_intent when present (instead of creating a new setup intent).
• Minor formatting-only changes (line wrapping / lint) in a few places.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
libs/payments/stripe/src/lib/stripe.client.ts	Adds a Stripe client wrapper for confirming an existing SetupIntent.
libs/payments/customer/src/lib/setupIntent.manager.ts	Adds a manager method to confirm a SetupIntent with a confirmation token.
libs/payments/cart/src/lib/checkout.service.ts	Uses pending_setup_intent on the subscription to drive setup intent confirmation path during checkout.

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