2.2.0

Added — sibling addons can put what they know on the contact screen

The contact page is where somebody goes to answer "who is this person and what
is going on with them", and a good deal of that lives outside LeadHub: which
mailing lists they are on, which automations they are enrolled in, what a
webhook last said about them. None of it could appear there, because the only
way would have been for this addon to know about its siblings — and the
direction of that dependency is the one thing this family keeps straight.
Marketing requires LeadHub; LeadHub requires nobody.

So the sibling registers instead:

LeadHub::registerContactPanel('marketing.subscriptions', function ($contact) {
    return [
        'heading' => __('Mailing lists'),
        'empty' => __('Not on any mailing list.'),
        'rows' => [[
            'label' => 'Der Chorleiter-Brief',
            'url' => cp_route('marketing.lists.show', 'chorleiter-brief'),
            'meta' => 'since March',
            'badge' => ['text' => 'Subscribed', 'color' => 'green'],
        ]],
    ];
});

The shape is deliberately dumb — a heading, rows of label/badge/meta, an
optional action — rather than a component name or a slot. A registry that
accepted markup would make every contributor's Vue build a dependency of this
page, and the first one to ship a broken bundle would take the screen with it.

A contributor that throws is logged and left out, never propagated: this runs
while the contact screen renders, and a sibling mid-upgrade must not be able to
500 the page somebody opened to read a phone number. One that returns null, or a
panel with neither rows nor an empty state, is simply not shown — "nothing to
say" is a legitimate answer and an empty box is not.

goldnead/statamic-marketing 2.6.0 is the first user: it lists the mailing
lists a contact is on, with their status and since when.