feat: Add POST endpoint signup4

app/api/endpoints/signup4.py

@@ -0,0 +1,12 @@
+from fastapi import APIRouter, HTTPException
+from pydantic import BaseModel
+
+router = APIRouter()
+
+class UserRegistration(BaseModel):
+    username: str
+    password: str
+    email: str
+@router.post("/signup")
+async def signup(user: UserRegistration):
+    return {"message": "User registered successfully", "user": user.username}