fix(signup): send first_name and last_name instead of full_name

- Backend now expects first_name and last_name separately
- Remove full_name field from registration payload

src/routes/signup.tsx

@@ -209,7 +209,8 @@ export default function SignupRoute() {
         headers: { "Content-Type": "application/json", Accept: "application/json" },
         credentials: "include",
         body: JSON.stringify({
-          full_name: `${firstName().trim()} ${lastName().trim()}`.trim(),
+          first_name: firstName().trim(),
+          last_name: lastName().trim(),
           email: email().trim().toLowerCase(),
           password: password(),
           phone: "",