Update payment link

## Update payment link Partially updates an existing payment link owned by the authenticated store. The body is a partial of the create DTO (all fields optional), and the supplied fields are shallow-merged over the link's existing `Data` blob. ### Behavior & side-effects - The link is looked up by `:id` scoped to `user.store_id` (404 if not found for this store). - `PaymentRequestLifecycleService.assertUpdatable` runs — the request must be in an updatable state (e.g. not COMPLETED/EXPIRED/DEACTIVATED), otherwise the update is rejected. - `assertImmutableFieldsUnchanged` runs — fields considered immutable once invoices exist for the link cannot be changed; attempting to change them fails. - If `appId` is supplied it replaces the current app association; otherwise the existing `AppId` is preserved. - Remaining fields are merged into the existing data (`{ ...oldData, ...data }`). ### Authentication - Send the merchant API key in the **`x-api-key`** header (alias `x-account-api-key`). - Requires scope **`Merchant.payment_link.update`**. - Optionally scope the key to a specific store/account with the **`x-application-account-id`** header (alias `x-account-id`) or the `application_account_id` / `account_id` query param. ### Path params - `id` — the payment link (payment request) id. ### Body (application/json) Any subset of the create-payment-link fields (see the Create payment link endpoint for the full field list, types, and conditional constraints). All fields are optional here (`PartialType`). Unknown properties are stripped by the global whitelist ValidationPipe. ### Response `200 OK` with the updated, presented `PaymentLinkResponseDto`. --- **Notas:** Deprecated alias paths PATCH /v1/payment-links/:id and PATCH /v1/payment-link/:id route to this same handler. Full body field list, types and conditional constraints are identical to the Create payment link endpoint (this DTO is PartialType(CreatePaymentLinkDto)); only a representative subset is enumerated here. Update is rejected if the link is not in an updatable lifecycle state (assertUpdatable) or if immutable fields are changed after invoices exist (assertImmutableFieldsUnchanged).