Fixes: 1) Remove 'recently_viewed' ManyToManyField from User model and related migration; 2) Correct handling of product addition in 'recently_viewed' logic.
Extra: Refactor 'recently_viewed' to use cache instead of database field; cleanup unused imports and model attributes.
Updated the API version from 2.5.0 to 2.6.0 in the DRF settings for consistency across configurations. Reformatted migration files for better readability, ensuring consistency in code style and improving maintainability. These changes do not alter functionality but enhance clarity and documentation.
