Add FastAPI backend with agent system

backend/app/schemas/auth.py

@@ -0,0 +1,26 @@
+from pydantic import BaseModel, EmailStr
+
+
+class UserCreate(BaseModel):
+    email: EmailStr
+    password: str
+    full_name: str | None = None
+
+
+class UserOut(BaseModel):
+    id: str
+    email: str
+    full_name: str | None
+    is_active: bool
+    is_superuser: bool
+
+    model_config = {"from_attributes": True}
+
+
+class Token(BaseModel):
+    access_token: str
+    token_type: str = "bearer"
+
+
+class TokenPayload(BaseModel):
+    sub: str