Find top BigCommerce customers with no open Nutshell lead

**Objective:** Find the top `{top-n}` BigCommerce customers by spend over the last `{lookback-days}` days (default 90, top 10) who have no open lead in Nutshell.

**Step 1: Read recent orders**

Call `bigcommerce-get-order` with `date-created.from` set to today minus `{lookback-days}` days and `max-records` 250. Group by `customer-id`, summing `total-including-tax` and subtracting `refunded-amount`. Ignore customer-id 0 (guest orders). Take the top `{top-n}`.

**Step 2: Identify them**

For each, call `bigcommerce-get-customer` with `id` set to the `customer-id` to get `name`, `email` and `company`.

**Step 3: Look for a CRM lead**

Call `nutshell-get-contact` with `name` set to the customer name and confirm the match by `emails`. If found, call `nutshell-get-lead` with `person-id` set to the contact `id` and `status` set to open. If the contact is missing or has no open lead, flag the customer.

**Step 4: Report**

Report the flagged customers ranked by net spend: name, company, net spend, order count, last order date, and whether the cause is "no CRM contact" or "no open lead". Also list the top customers who do have an open lead, briefly.

**Rules & Guidelines:**

* `bigcommerce-*` tools are on the bigcommerce server and `nutshell-*` tools are on the nutshell server. Both servers must be connected.
* This is read-only. Never call any add, update or delete tool on either server (for example `bigcommerce-customer-update`, `nutshell-add-person`, `nutshell-update-lead`, `nutshell-delete-company`).

**Validation:**

* If the 250 order cap was reached, say the ranking may be incomplete.
* If no orders exist in the period, say so and stop.