docs: update Bruno API tests for device registration and admin registration

- Fix device registration API test parameters
- Update admin user registration test with proper fields
- Ensure API tests match current endpoint behavior
- Improve API documentation accuracy

bruno/user/admin/Register Admin User.bru

@@ -12,9 +12,9 @@ post {
 
 body:json {
   {
-    "email": "admin@example.com",
-    "username": "admin",
-    "password": "admin123",
+    "email": "admin2@example.com",
+    "username": "admin2",
+    "password": "!Admin@123",
     "first_name": "Admin",
     "last_name": "User",
     "role": "admin"