Add ActiveRecord, customer dashboard, separate DB architecture

- Re-enable ActiveRecord pointing at Neon Postgres
- Add Customer model with stripe_customer_id, email, slug, status
- Add dashboard controller and Apple ID-style device view
- Redirect checkout success to /dashboard
- Webhook now calls /instances, parses response, creates Customer in Rails DB
- Add MIT License

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

bin/docker-entrypoint

@@ -1,8 +1,3 @@
 #!/bin/bash -e
 
-# If running the rails server then create or migrate existing database
-if [ "${1}" == "./bin/rails" ] && [ "${2}" == "server" ]; then
-  ./bin/rails db:prepare
-fi
-
 exec "${@}"