Fix first user registration not calling register endpoint

When isFirstUser is true, the form displayed "Create Admin Account"
but still called the login endpoint instead of register. Now checks
both isRegister and isFirstUser to determine which endpoint to call.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: clucraft

client/src/pages/Login.tsx

@@ -45,7 +45,7 @@ export default function Login({ onLogin }: LoginProps) {
     setLoading(true);
 
     try {
-      if (isRegister) {
+      if (isRegister || isFirstUser) {
         const response = await authApi.register(email, password, name);
         setIsRegister(false);
         setError('');