Wave 1

[mayskii]

Implemented the first wave of the Task List API:

• Added Task model (id, title, description, completed_at).
• Added from_dict and to_dict helper methods.
• Created routes: POST /tasks, GET /tasks, GET /tasks/, PUT /tasks/, DELETE /tasks/.
• Added validate_model for ID checks and 400/404 handling.
• Applied database migration for Task.
• All Wave 1 tests pass.