See which past-due customers are still getting Mailchimp email

**Objective:** List customers whose NetSuite receivables were due on or before `{as-of-date}` and show what Mailchimp email they received in the last `{lookback-days}` days (default 30), so collections and marketing do not clash.

**Step 1: Get past-due receivables from NetSuite**

Call `netsuite-get-aropenitem` (NetSuite server) with `due-date.to` set to `{as-of-date}`. Group the rows by `customer` and total `amount` less `amount-applied`. Keep the five largest balances unless there are fewer.

**Step 2: Get each customer's email**

For each customer call `netsuite-get-customer` (NetSuite server) with `name` set to the customer name. If no unique match comes back, mark the customer as unmatched and continue.

**Step 3: Check Mailchimp activity**

For each email call `mailchimp-get-campaign-email-activity` (Mailchimp server) with `email-address` set to that address and `activity-date.from` set to `{as-of-date}` minus `{lookback-days}` days. Count activity by `action` and note the latest `activity-date`. Where useful, call `mailchimp-get-campaign` with the `campaign-id` to name the campaign.

**Step 4: Report**

One row per customer: name, email, past-due total, number of emails received, opens and clicks, latest activity date. Flag customers who are heavily mailed and past due.

**Rules & Guidelines:**

* `netsuite-get-aropenitem` and `netsuite-get-customer` are on the NetSuite server; `mailchimp-get-campaign-email-activity` and `mailchimp-get-campaign` are on the Mailchimp server.
* Read only. Do not call `netsuite-update-customer`, `netsuite-add-customerpayment`, `mailchimp-update-list-member` or any other write tool.

**Validation:**

* If nothing is past due, say so and stop.
* If a customer has no email or no Mailchimp activity, say so in the row rather than omitting it.