fix(notifications): add unenrollment notification trigger

[faisalahammad]

Summary

Adds a new unenrollment notification trigger that fires when a student is removed from a course or membership. Supports both popup (basic) and email delivery, with all subscribers disabled by default so existing sites are not opted in.

Fixes #3141

Changes

includes/notifications/controllers/class.llms.notification.controller.unenrollment.php (new)

Before: no controller existed for the unenrollment event.

After:

class LLMS_Notification_Controller_Unenrollment extends LLMS_Abstract_Notification_Controller {
    public $id = 'unenrollment';
    protected $action_accepted_args = 4;
    protected $action_hooks = array(
        'llms_user_removed_from_course',
        'llms_user_removed_from_membership',
    );
    // action_callback() captures user_id + post_id and dispatches the notification.
    // get_subscriber() resolves 'author' (course/membership author) and 'student' (the unenrolled user).
    // set_subscriber_options() returns 'no' defaults for all subscribers.
}

Why: mirrors the existing enrollment controller pattern so admins configure one notification for both post types. Uses llms_user_removed_from_membership rather than the _level form (the _level hook was removed in 6.0.0). Accepts 4 args because the unenrollment action passes $user_id, $post_id, $trigger, $new_status.

includes/notifications/views/class.llms.notification.view.unenrollment.php (new)

Before: no view existed for the unenrollment event.

After:

class LLMS_Notification_View_Unenrollment extends LLMS_Abstract_Notification_View {
    public $trigger_id = 'unenrollment';
    protected $basic_options = array( 'auto_dismiss' => 10000, 'dismissible' => true );
    // Merge codes: {{TITLE}}, {{TYPE}}, {{STUDENT_NAME}}
    // Icon: negative variant.
    // Body: "{{STUDENT_NAME}} has been unenrolled from {{TITLE}}."
    // Subject: "{{STUDENT_NAME}} unenrolled from {{TITLE}}"
    // Title: "{{TYPE}} unenrollment"
}

Why: same merge-code and formatting conventions as the enrollment view. Negative icon visually signals removal. The popup auto-dismisses and is manually dismissible like the rest of the basic notifications.

includes/notifications/class.llms.notifications.php

Before: $triggers array ended with subscription_cancelled followed by upcoming_payment_reminder.

After: 'unenrollment' inserted between them to keep alphabetical order.

Why: the loader pulls the controller and view from their conventional paths once the trigger is registered, so no other registration is needed.

.changelogs/issue-3141.yml (new)

significance: minor
type: added
entry: "Added unenrollment notification trigger (popup and email) for courses and memberships, disabled by default."

Why: the project's changelog tooling only picks up files ending in .yml; this matches the contribution workflow.

Testing

Test 1: registration

1. WP Admin → LifterLMS → Settings → Notifications.
2. Confirm a new "Unenrollment" row appears.

Result: Works as expected.

Test 2: defaults disabled

1. Open the Unenrollment notification.
2. Confirm Student, Author, and Custom Email subscribers are all unchecked.

Result: Works as expected.

Test 3: course unenrollment

1. Enable Student (basic) and Student (email).
2. Enroll a test student in a course, then unenroll them from the Students tab.
3. Log in as the student and load a LifterLMS page.

Result: popup appears with the course title and the negative icon; the student receives the email.

Test 4: membership unenrollment

1. Repeat Test 3 with a membership.

Result: same popup and email behavior, with {{TYPE}} resolving to "Membership".

Test 5: silent on hard delete

1. Programmatically call llms_delete_student_enrollment() which fires the llms_user_enrollment_deleted hook (not the unenrollment hook).

Result: no notification is sent.