Trial-ending reminder email (MAIL-05).
Triggered by the customer.subscription.trial_will_end Stripe webhook
(usually 3 days before trial_end). Uses the shared transactional MJML
scaffold + Accrue.Invoices.Components.footer/1 via HtmlBridge.
Summary
Functions
Returns the raw MJML template. Useful for debugging rendering issues.
Safely render the MJML template using Phoenix.HTML