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>

config/routes.rb

@@ -2,6 +2,7 @@ Rails.application.routes.draw do
   root "pages#home"
   get  "/pricing",  to: "pages#pricing"
   get  "/success",  to: "pages#success"
+  get  "/dashboard", to: "dashboard#show"
 
   post "/checkout/create_session", to: "checkout#create_session"
   post "/checkout/webhook",        to: "checkout#webhook"