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>

app/controllers/dashboard_controller.rb

@@ -0,0 +1,14 @@
+class DashboardController < ApplicationController
+  def show
+    if params[:session_id].present?
+      stripe_session = Stripe::Checkout::Session.retrieve(params[:session_id])
+      @customer = Customer.find_by(stripe_customer_id: stripe_session.customer)
+    elsif params[:email].present?
+      @customer = Customer.find_by(email: params[:email])
+    else
+      redirect_to root_path
+    end
+  rescue Stripe::StripeError
+    redirect_to root_path
+  end
+end