Refactor and reorganize Alembic and database configuration.

Moved Alembic files into the `app/alembic` directory and updated related paths. Consolidated database configuration in `config.py`, leveraging environment variables and ensuring centralized management. Updated Docker Compose to include `.env` files, providing a more consistent environment setup.

backend/app/core/database.py

@@ -1,11 +1,11 @@
 from sqlalchemy import create_engine
 from sqlalchemy.ext.declarative import declarative_base
 from sqlalchemy.orm import sessionmaker
-import os
 
-SQLALCHEMY_DATABASE_URL = os.getenv("DATABASE_URL", "postgresql://postgres:postgres@db:5432/app")
+from app.core.config import settings
 
-engine = create_engine(SQLALCHEMY_DATABASE_URL)
+# Use the database URL from settings
+engine = create_engine(settings.database_url)
 SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
 
 Base = declarative_base()