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

app/views/shared/_flash_messages.html.erb

@@ -1,21 +1,21 @@
 <% if flash.any? %>
-  <div class="flash-messages-container" style="position: relative; width: 100%; display: flex; justify-content: center; padding: var(--space-4); margin-top: var(--space-4);">
-    <div style="width: 100%; max-width: 600px;">
-      <% flash.each do |type, message| %>
-        <div class="notification <%= flash_class(type) %>"
-             data-controller="flash-message"
-             style="display: flex; align-items: center; gap: var(--space-3); padding: var(--space-4); border-radius: var(--radius-lg); margin-bottom: var(--space-3); font-weight: 500; width: 100%; box-sizing: border-box;">
-          <div class="notification-icon" style="display: flex; align-items: center; flex-shrink: 0;">
-            <%= flash_icon(type) %>
+  <div class="container">
+    <div class="relative w-full flex justify-center p-4 mt-4">
+      <div class="w-full max-w-xl">
+        <% flash.each do |type, message| %>
+          <div class="notification <%= flash_class(type) %> flex items-center gap-3 p-4 rounded-lg mb-3 font-medium w-full box-border"
+              data-controller="flash-message">
+            <div class="notification-icon flex items-center shrink-0">
+              <%= flash_icon(type) %>
+            </div>
+            <span class="flex-1"><%= message %></span>
+            <button data-action="click->flash-message#close"
+                    class="bg-transparent border-none cursor-pointer p-1 text-inherit opacity-70 transition-opacity duration-200">
+              <i data-lucide="x" class="w-4 h-4"></i>
+            </button>
           </div>
-          <span style="flex: 1;"><%= message %></span>
-          <button data-action="click->flash-message#close"
-                  style="background: none; border: none; cursor: pointer; padding: var(--space-1); color: inherit; opacity: 0.7; transition: opacity 0.2s;">
-            <i data-lucide="x" style="width: 16px; height: 16px;"></i>
-          </button>
-        </div>
-      <% end %>
+        <% end %>
+      </div>
     </div>
   </div>
-
 <% end %>