Add .env-example file and update configuration for environment variables

- Created .env-example for environment variable setup
- Updated README to reflect changes in .env file creation
- Modified config.py to include new environment variables and DATABASE_URL property
- Enhanced database.py with connect and disconnect functions
- Updated main.py to manage database connection lifecycle
- Adjusted compose.yaml for consistent environment variable usage

app/database.py

@@ -1,11 +1,22 @@
+from typing import AsyncGenerator
 from sqlalchemy.ext.asyncio import create_async_engine, AsyncSession
 from sqlalchemy.orm import sessionmaker
-from sqlalchemy import text
 from app.config import settings
 
-engine = create_async_engine(settings.DATABASE_URL, echo=True)
+engine = create_async_engine(settings.DATABASE_URL, echo=settings.DEBUG)
 AsyncSessionLocal = sessionmaker(engine, class_=AsyncSession, expire_on_commit=False)
 
-async def get_db():
+async def connect():
+    pass  # engine initializes at module level
+
+async def disconnect():
+    await engine.dispose()
+
+async def get_db() -> AsyncGenerator[AsyncSession, None]:
     async with AsyncSessionLocal() as session:
-        yield session
+        try:
+            yield session
+            await session.commit()
+        except Exception:
+            await session.rollback()
+            raise