feat: refactor inactive user reminders + improve disable/enable flows

[Mubangizi]

Description

• Improved disable and enable logic, added DetailedModelMixin that introduces shared attributes and is used by Users, Projects and Apps
• Improved querying and filtering for inactive users, added more robust filter options
• Added a CLI command send-inactive-user-reminders to handle sending of reminders to inactive users .
• Hardened reminder delivery by ensuring a valid Flask app context is used for async email threads.
• Improved email templates for user/project/app disable/enable and inactive_user_reminder messages.