This commit includes the foundational backend implementation for a to-do list
web application with employee and manager roles.

Key features implemented:
- Project structure setup using Flask blueprints.
- Database models for Users and Tasks with Flask-SQLAlchemy.
- User authentication (registration, login, logout) with password hashing.
- Role-based access control (employee, manager).
- Employee features:
    - Create, view, list, update, delete personal tasks.
    - Mark tasks as complete.
- Manager features:
    - View all tasks in the system.
    - Assign tasks to employees.
    - Approve tasks marked as complete by employees.

The backend logic for these features is in place. UI implementation
(HTML templates) and comprehensive unit tests are the next steps.