feat: add user model and registration endpoint

backend/app/security.py

@@ -0,0 +1,15 @@
+from argon2 import PasswordHasher
+from argon2.exceptions import VerifyMismatchError
+
+_hasher = PasswordHasher()
+
+
+def hash_password(password: str) -> str:
+    return _hasher.hash(password)
+
+
+def verify_password(password: str, password_hash: str) -> bool:
+    try:
+        return _hasher.verify(password_hash, password)
+    except VerifyMismatchError:
+        return False