Find paid BigCommerce orders that were never invoiced

**Objective:** List BigCommerce orders created since `{date-from}` that are paid or shipped but have no FreshBooks invoice, so they can be billed.

**Step 1: Read the orders**

Call `bigcommerce-get-order` (bigcommerce server) with `date-created.from` set to `{date-from}` and `payment-status` set to `{payment-status}` (default: paid). Keep `id`, `billing-email`, `billing-first-name`, `billing-last-name`, `total-including-tax`, `currency-code` and `date-created`.

**Step 2: Check FreshBooks**

For each distinct `billing-email` call `freshbooks-get-client` (freshbooks server) with `email` set to it. When a client exists, call `freshbooks-get-invoice` (freshbooks server) with `customer-id` set to the client `id` and `create-date.from` set to `{date-from}`. An order counts as billed if an invoice has `po-number` equal to the order `id`, or the same `amount` and `currency-code`.

**Step 3: Report**

A table of unbilled orders: order id, date, email, total, and whether the customer already exists as a FreshBooks client (yes or no). Group them into "client exists" and "client missing". Finish with the count and total value.

**Rules & Guidelines:**

* `bigcommerce-get-order` is on the bigcommerce server. `freshbooks-get-client` and `freshbooks-get-invoice` are on the freshbooks server.
* Read-only. Never create clients or invoices from this prompt. Name the `invoice-bigcommerce-order` prompt as the next step.

**Validation:**

* If no orders match, say so and stop.
* An order whose invoice match is uncertain goes in a separate "needs review" list, not in the unbilled list.