implement initial backend structure with authentication, user management, and database integration

backend/app/models/auth.py

@@ -0,0 +1,22 @@
+"""Pydantic schemas for authentication endpoints."""
+from pydantic import BaseModel, EmailStr
+
+
+class RegisterRequest(BaseModel):
+    email: EmailStr
+    password: str
+
+
+class LoginRequest(BaseModel):
+    email: EmailStr
+    password: str
+
+
+class TokenResponse(BaseModel):
+    access_token: str
+    refresh_token: str
+    token_type: str = "bearer"
+
+
+class RefreshRequest(BaseModel):
+    refresh_token: str