Delete customer

## Delete customer Permanently deletes the customer identified by `id`, scoped to the authenticated store. ### Authentication - Send the merchant API key in the **`x-api-key`** header (alias `x-account-api-key`). - Requires the scope: **`Merchant.customer.delete`**. - Optionally scope the key with **`x-application-account-id`** (alias `x-account-id`) or the `application_account_id` / `account_id` query param. ### Path params - `id`: the customer UUID (must belong to the caller's store). ### Behavior - If the customer is not found for the store: **404 Not Found**. - On success returns a confirmation message object. - Note: the `customers` table has related `paymentRequests`; deleting a customer removes the customer row (foreign-key/cascade behavior governed by the database). --- **Notas:** Existence is verified against the caller's store before deletion (404 otherwise). Returns a { message } confirmation rather than the deleted entity.