Educational Web App Upgrade and Bug Fixes

Hi, I have an educational web application currently built with:

Backend: PHP 5, CodeIgniter 3
Database: MySQL 5
Frontend: HTML, CSS
Scripting: JavaScript, jQuery, Ajax
I’m looking for a technical specialist who can:

Fix existing issues / bugs in the application
Upgrade the technology stack (as needed) to modern, stable versions
Test the application thoroughly and resolve any resulting problems
Make required code and configuration changes to ensure everything works smoothly
Support future work—I plan to add AI plugins later, so experience with AI integrations is a plus.
Key Requirements
Strong experience with CodeIgniter 3 and PHP
Good knowledge of MySQL and database migrations
Ability to analyze, debug, and refactor legacy code
Experience with testing and deployment
Communication in English (clear updates/progress)
Deliverables
Working application after fixes and upgrades
Documentation of changes made (at least brief)
Test report / list of key test cases performed
If you’re confident you can handle this, please apply ASAP with:

Your relevant experience (links/portfolio if available)
Your estimated timeline and cost
Your proposed upgrade approach (brief)
Thank you.