CodeIgniter 3 → 4 Full Migration Experts can apply

I have an existing website built on CodeIgniter 3 that now needs to run on CodeIgniter 4. The goal is a like-for-like migration: every current page, controller, model, library, helper and route should work on CI4 without breaking any user-facing or admin features. All data structures must stay intact; if small refactors are required for CI4’s namespaces, routing or config conventions, please handle them while keeping the logic unchanged.

I will provide the full CI3 codebase and database schema. You return a clean CI4 project, fully tested and ready to drop onto the server (CLI, web routes, .env and composer all set up). Any legacy functions that CI4 has replaced should be rewritten the CI4 way rather than shimmed.

Please outline:
• Estimated timeframe for the migration
• How you plan to verify feature parity and fix regression issues
• Any post-handover support or bug-fix window you include

If you have successfully moved complete sites from CI3 to CI4 before, that’s a big plus—share a short example or two so I can confirm compatibility and code quality.