feat: Implement complete ticket purchasing flow with new TicketsController

- Create new TicketsController with actions for name collection, creation, and checkout
- Add dedicated ticket views (new.html.erb, checkout.html.erb, show.html.erb)
- Update ticket_selection_controller.js to handle form submission via AJAX
- Add store_cart endpoint in EventsController for session-based cart management
- Update routes to support new ticket flow: /tickets/new, /create, /checkout
- Fix attribute name consistency across views (title→name, starts_at→start_time)
- Add Stripe checkout integration with proper error handling
- Remove deprecated collect_names flow in favor of streamlined approach

The flow is now: Event selection → AJAX cart storage → Name collection → Checkout → Payment

Gemfile.lock

@@ -113,6 +113,9 @@ GEM
       responders
       warden (~> 1.2.3)
     dotenv (3.1.8)
+    dotenv-rails (3.1.8)
+      dotenv (= 3.1.8)
+      railties (>= 6.1)
     drb (2.2.3)
     ed25519 (1.4.0)
     erb (5.0.2)
@@ -412,6 +415,7 @@ DEPENDENCIES
   cssbundling-rails
   debug
   devise (~> 4.9)
+  dotenv-rails
   jbuilder
   jsbundling-rails
   kamal