Add missing Rillet customers to Mailchimp with opt-in

**Objective:** Add the Rillet customer emails that are not yet in the Mailchimp audience `{list-name}`, using member status `{member-status}` (default pending, which sends Mailchimp's opt-in confirmation).

**Step 1: Confirm the audience**

Call `mailchimp-get-list` with `name.contains` set to `{list-name}`. Continue only if exactly one audience matches; otherwise list the matches (or say there are none) and stop. Keep its `list-id`.

**Step 2: Find the gap**

* Call `rillet-get-customer-emails` (no filters).
* Call `mailchimp-get-list-member` with `list-name` set to the confirmed name and `max-records` covering the audience size.
* Match emails case-insensitively after trimming spaces. A Rillet customer can have several emails (`email-type`), and one email can appear on more than one Rillet customer: keep every pairing and say so in the report. Drop every email that already has a member row in ANY status, including unsubscribed and cleaned.

**Step 3: Show the plan and stop**

Present a table of the emails to add: email, Rillet customer name, `customer-id`, and the status they will get. State the total. Then ask the user to confirm. Do not write anything until they explicitly confirm; if they remove rows, use the edited list.

**Step 4: Add the members**

For each confirmed email, call `mailchimp-add-list-member` once with `list-id` from Step 1, `email-address` set to the email, and `status` set to the member status. Leave `first-name` and `last-name` empty, because Rillet stores the company name, not the person's name.

**Step 5: Confirm and report**

Call `mailchimp-get-list-member` with `list-name` and `email` for each added address and report: added, already present, and failed (with the error).

**Rules & Guidelines:**

* Tools named mailchimp- come from the mailchimp MCP server; tools named rillet- come from the rillet MCP server. If a tool from either server is missing, stop and say which server is not connected rather than working around it.
* The only key shared by the two systems is the email address. Mailchimp `customer-id` values (e-commerce store customers) are NOT Rillet customer ids; never pass one system's id into the other.
* The only write tool this prompt may call is `mailchimp-add-list-member` on the mailchimp server, and only after the user confirms the plan in Step 3.
* Never call `mailchimp-update-list-member`, and never add or re-subscribe anyone whose existing status is unsubscribed or cleaned. Doing so overrides their consent.
* Do not call any Rillet tool whose name starts with rillet-add-, rillet-update-, rillet-apply-, rillet-unapply-, rillet-record-, rillet-set- or rillet-setup-.

**Validation:**

* If `{member-status}` is empty, use pending. Accept only pending, subscribed or transactional; for anything else, ask the user to choose.
* Use subscribed only if the user states they already hold marketing consent for these contacts.
* If the gap is empty, report that every Rillet customer email is already in the audience and stop.
* If an add fails because the address is invalid or previously removed by Mailchimp, record it as failed and continue with the rest.