- Added a new `content` field to the `cards` table in the database.
- Updated the card creation and update schemas to include the `content` field.
- Modified the card service to handle the new `content` field in create and update operations.
- Enhanced search functionality to include the `content` field.
- Updated migrations to reflect the addition of the `content` field in the database schema.
- Added the `marked` package for potential markdown processing in the content field.
