🚀 Add Postgres Service and Database Support

[arcane-engine]

This PR adds database support to the project by integrating Postgres, SQLAlchemy, and Alembic.

Docker and Dependencies

• Add a Postgres service to docker-compose.yaml.
• Update requirements.txt with SQLAlchemy (2.0.28) and Alembic (1.13.1).

File Restructuring

• Move app.py to app/main.py.

Database Integration

• Create crud.py, database.py, models.py, and schemas.py in the app directory with relevant content.
• Add Alembic migration scripts in the migrations directory.

Your project now has database support with SQLAlchemy and Alembic.