API HTTP 409 if mail is in unconfirmed state

[TheDanniCraft]

Version:

• listmonk: 4.1.0
• OS: linux

Description of the bug and steps to reproduce: When attempting to add a subscriber to a list with double opt-in enabled, the API returns a 409 Conflict if the email already exists — even if the subscriber is in a pending (unconfirmed) state.

While a 409 makes sense when a subscriber is already confirmed, it becomes problematic for pending users. If the subscriber has not confirmed their email yet, it would be helpful if listmonk either:

1. Resent the double opt-in confirmation email automatically, or
2. Add a resend_confirmation: true option to the api

Steps to reproduce:

1. Subscribe a new email to a list with double opt-in enabled.
2. Do not click the confirmation link.
3. Attempt to subscribe the same email again via the API.
4. A 409 Conflict is returned, but no confirmation email is resent.

Screenshots: If applicable, add screenshots to help explain your problem.