Add init_db script for async database initialization and extensive tests for session management

- Added `init_db.py` to handle async database initialization with the creation of the first superuser if configured.
- Introduced comprehensive tests for session management APIs, including session listing, revocation, and cleanup.
- Enhanced CRUD session logic with UUID utilities and improved error handling.

backend/app/crud/session.py

@@ -2,6 +2,7 @@
 Async CRUD operations for user sessions using SQLAlchemy 2.0 patterns.
 """
 import logging
+import uuid
 from datetime import datetime, timezone, timedelta
 from typing import List, Optional
 from uuid import UUID

backend/app/init_db.py

@@ -0,0 +1,92 @@
+# app/init_db.py
+"""
+Async database initialization script.
+
+Creates the first superuser if configured and doesn't already exist.
+"""
+import asyncio
+import logging
+from typing import Optional
+
+from app.core.config import settings
+from app.core.database import SessionLocal, engine
+from app.crud.user import user as user_crud
+from app.models.user import User
+from app.schemas.users import UserCreate
+
+logger = logging.getLogger(__name__)
+
+
+async def init_db() -> Optional[User]:
+    """
+    Initialize database with first superuser if settings are configured and user doesn't exist.
+
+    Returns:
+        The created or existing superuser, or None if creation fails
+    """
+    # Use default values if not set in environment variables
+    superuser_email = settings.FIRST_SUPERUSER_EMAIL or "admin@example.com"
+    superuser_password = settings.FIRST_SUPERUSER_PASSWORD or "admin123"
+
+    if not settings.FIRST_SUPERUSER_EMAIL or not settings.FIRST_SUPERUSER_PASSWORD:
+        logger.warning(
+            "First superuser credentials not configured in settings. "
+            f"Using defaults: {superuser_email}"
+        )
+
+    async with SessionLocal() as session:
+        try:
+            # Check if superuser already exists
+            existing_user = await user_crud.get_by_email(session, email=superuser_email)
+
+            if existing_user:
+                logger.info(f"Superuser already exists: {existing_user.email}")
+                return existing_user
+
+            # Create superuser if doesn't exist
+            user_in = UserCreate(
+                email=superuser_email,
+                password=superuser_password,
+                first_name="Admin",
+                last_name="User",
+                is_superuser=True
+            )
+
+            user = await user_crud.create(session, obj_in=user_in)
+            await session.commit()
+            await session.refresh(user)
+
+            logger.info(f"Created first superuser: {user.email}")
+            return user
+
+        except Exception as e:
+            await session.rollback()
+            logger.error(f"Error initializing database: {e}")
+            raise
+
+
+async def main():
+    """Main entry point for database initialization."""
+    # Configure logging to show info logs
+    logging.basicConfig(
+        level=logging.INFO,
+        format="%(asctime)s - %(name)s - %(levelname)s - %(message)s"
+    )
+
+    try:
+        user = await init_db()
+        if user:
+            print(f"✓ Database initialized successfully")
+            print(f"✓ Superuser: {user.email}")
+        else:
+            print("✗ Failed to initialize database")
+    except Exception as e:
+        print(f"✗ Error initializing database: {e}")
+        raise
+    finally:
+        # Close the engine
+        await engine.dispose()
+
+
+if __name__ == "__main__":
+    asyncio.run(main())