Migrate from Devise to Rails authentication generator

A practical guide to migrating from Devise to Rails 8's built-in authentication generator. Covers the full migration process including running the generator, creating a database migration to rename columns and remove Devise-specific fields, restoring the User model with has_secure_password, updating routes, adding current_user helpers to ApplicationController, fixing test helpers and fixtures, replacing Devise path helpers in views, updating system tests to remove Warden dependency, and finally removing the Devise gem entirely.