{% comment %} Base email layout — shared shell (header/logo, body slot, footer) for every stapel-notifications email. Branding is driven by STAPEL_NOTIFICATIONS: LOGO_URL, BRAND_PRIMARY, BRAND_PRIMARY_DARK, BRAND_BG, BRAND_TEXT — threaded in as logo_url / brand_* template variables by services.process_notification. Type templates extend this and fill {% block content %}; override {% block preheader %} (defaults to the subject) or {% block footer %} when needed. The footer picks the unsubscribe variant automatically whenever an unsubscribe_url is present (non-auth groups). {% endcomment %}