Add Mailchimp contacts without re-subscribing anyone who opted out

**Objective:** Add `{email-address}` (name {contact-name}, if given) to the Mailchimp audience `{list-name}`, and to the tag {tag-name} if one is given, without duplicating an existing member or re-subscribing someone who opted out.

**Step 1: Resolve the audience**

Call `mailchimp-get-list` with `name` set to the audience name. If nothing matches, retry with `name.contains`. If more than one audience matches, list them and stop. Keep the list-id.

**Step 2: Check for an existing member**

Call `mailchimp-get-list-member` with `email` set to the address and `list-name` set to the audience.

* `subscribed` or `pending`: the contact is already in the audience. Do not add them. Go to Step 3 only if a tag was given.
* `unsubscribed` or `cleaned`: stop. Do not re-add or re-subscribe them. Explain that the contact has to opt in again themselves, for example through a signup form.
* Not found: continue.

**Step 3: Resolve the tag**

If a tag name was given, call `mailchimp-get-segment` with `list-id` and `name` set to the tag name. It must exist and its type must be `static`. If not, tell the user and ask whether to continue without the tag.

**Step 4: Confirm**

Show the user what will be written: audience, email, first and last name (split from the full name), status and tag. The status is `pending` by default, which sends a double opt-in confirmation email. Use `subscribed` only if the user states that the contact has already given consent. Ask the user to confirm and wait for the answer.

**Step 5: Act**

Only after the user confirms:

* If the contact is new, call `mailchimp-add-list-member` once with `list-id`, `email-address`, `status`, and `first-name` and `last-name` if known.
* If a tag was resolved, call `mailchimp-add-segment-member` once with `segment-id`, `list-id` and `email-address`.

**Step 6: Verify**

Call `mailchimp-get-list-member` with `email` and `list-name` and report the contact's status and tags.

**Rules & Guidelines:**

* The only write tools allowed are `mailchimp-add-list-member` and `mailchimp-add-segment-member`, each at most once.
* Never call `mailchimp-update-list-member`, so an existing contact's status and details are never changed.

**Validation:**

* If the email address is not a valid address, say so and stop.
* If the add call fails because the contact already exists, report it rather than retrying.