MANUAL TESTING , OPTIMIZATION AND CHECK FOR RESPONSIVENSESS

I have an existing web application built using React.js (frontend), Node.js (backend), and PostgreSQL (database), and I am looking for an experienced expert to thoroughly manually test the entire application end-to-end, identify and resolve all bugs and errors (frontend and backend), and make the complete UI fully responsive across mobile, tablet, and desktop devices. The work includes detailed manual testing of all modules, user flows, validations, APIs, and edge cases, fixing all discovered issues, resolving console/runtime/server errors, improving UI/UX where required, and ensuring stable performance. The developer must also provide proper documentation, including a structured bug report, details of fixes performed, and a final QA checklist confirming successful testing. Strong experience in manual QA testing, React, Node.js, responsive design (CSS/Flexbox/Grid/Bootstrap/Tailwind), and clear documentation is mandatory.