Replace WYSIWYG editor with Markdown editor across all relevant models and admin fields. Add utilities for rendering and stripping markdown. Adjust serializers, views, and templates to support markdown content. Introduce `PastedImage` model and upload endpoint for handling inline image uploads in markdown.
This change simplifies content formatting while enhancing flexibility with markdown support.
Includes detailed OpenAPI schemas for unsubscribe (GET and POST) and tracking pixel (GET) endpoints, supporting email compatibility and event tracking. Added support for RFC 8058-compliant one-click unsubscribe functionality and transparent image-based email tracking.
