Running a two-sided marketplace on shared hosting: PHP 7.4, no framework, no cron

I run Kimusta, a marketplace for local services in Turkey. Someone posts what they need (a move, a deep clean, a broken boiler), vetted service providers send quotes, and the customer compares them. The interesting part is not the product. The interesting part is that it runs on cheap shared hosting: PHP 7.4 behind LiteSpeed, MariaDB 10.3, no framework, no Node runtime, no Redis, no queue worker, and no guarantee that cron will actually fire. Here is what that constraint forced me to build, and the bugs it produced.