handle already existing users

database.py

@@ -49,11 +49,17 @@ def close() -> None:
 
 def register(user: User) -> None:
     """Registers a new user in the database."""
+    try:
         cursor.execute(
             "INSERT INTO users (name, password) VALUES (?, ?)",
             (user.name,
              security.hash_password(user.password)))
         connection.commit()
+    except sqlite3.IntegrityError:
+        raise HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            detail="User already exists"
+        )
 
 
 def get_user_by_token(request: Request) -> User: