Get Available Tracking Domains

Get list of available tracking domains.

Returns all configured tracking domains that can be selected for link tracking.

Required Scopes: Requires authentication (any authenticated user)

Database: None (reads from config)

Response:

{
    "domains": [
        {
            "id": "sendseven",
            "domain": "c.sendseven.com",
            "format": "/{code}",
            "label": "SendSeven (c.sendseven.com)",
            "default": true
        },
        ...
    ],
    "default_domain": "c.sendseven.com"
}