Respect every Mailchimp unsubscribe in DonorPerfect too

**Objective:** Find everyone who unsubscribed from a Mailchimp campaign in the last `{lookback-days}` days (default 30), match them to DonorPerfect donors by email, and set the DonorPerfect flag `{flag}` on each so staff know not to email them.

**Step 1: Validate the flag**

Call `donorperfect-get-code` with `code` set to `{flag}`. Confirm a match whose field name is the flag field and that is not inactive. If there is none, list close matches with `description.contains` and stop.

**Step 2: Read the unsubscribes**

Call `mailchimp-get-campaign-unsubscribe` with `unsubscribe-date.from` set to `{lookback-days}` days before today. De-duplicate by email, keeping the latest date, the campaign name and the reason.

**Step 3: Match to donors and skip already flagged**

For each email, call `donorperfect-get-donor` with `email` (fall back to `donorperfect-get-address` with `email`). For each matched donor, call `donorperfect-get-flag` with `donor-id` and `flag` set to `{flag}`; skip donors who already carry it.

**Step 4: Confirm before writing**

Show the donors to flag (donor id, name, email, unsubscribe date, campaign, reason) and the unmatched email count. Ask the user to confirm. Do not write until they do.

**Step 5: Set the flag**

For each confirmed donor, call `donorperfect-set-flag` with `donor-id` and `flag` set to `{flag}`. Record any failure and continue.

**Step 6: Report**

Flagged, already flagged, failed and unmatched counts, with the flagged rows.

**Rules & Guidelines:**

* `mailchimp-get-campaign-unsubscribe` is on the mailchimp server. `donorperfect-get-code`, `donorperfect-get-donor`, `donorperfect-get-address`, `donorperfect-get-flag` and `donorperfect-set-flag` are on the donorperfect server.
* `donorperfect-set-flag` is the only write, only after Step 4 confirmation. Do NOT call `mailchimp-update-list-member` or `mailchimp-add-list-member`: never resubscribe anyone. Do NOT call `donorperfect-save-donor`.

**Validation:**

* If there are no unsubscribes in the window, say so and stop.
* If one email matches several donors, list them and flag none of them until the user picks.