🌟 Allow customization of the email template used for attendee messages #1140
Description
Is your feature request related to a problem? Please describe.
When sending a message to attendees, the message body is wrapped in a fixed Blade template that includes a hardcoded legal footer ("You are receiving this communication because you are registered as an attendee..."). There is no way to customize this wrapper — not the footer text, not the layout, not the surrounding content.
By contrast, the ORDER_CONFIRMATION and ATTENDEE_TICKET email types are fully customizable via the Email Templates UI.
Describe the solution you'd like
Add an EVENT_MESSAGE type to the email template system so that organizers can customize the full template used when sending messages to attendees, with the same Liquid token support available in other templates.
Additional context
The current template is located at resources/views/emails/event/message.blade.php. The email template customization system is already in place (EmailTemplateType, EmailTemplateService, LiquidTemplateRenderer) — this would extend it to cover attendee messages.