Authentication from Scratch in Rails

Welcome back to the "Ruby for AI" series. This is the part where Rails starts feeling like a real product framework instead of just a nice way to render HTML. If you want to build AI apps people can actually use, you need authentication. Not because auth is glamorous. It isn't. But because the second you have user-specific prompts, saved conversations, uploaded files, billing, or private workflows, you need a way to know who is who. In this post, we will build authentication in Rails from scrat