feat: Complete hybrid image upload system with URL compatibility

- Add hybrid image system supporting both file uploads and URL images
- Implement Active Storage for file uploads while preserving existing URL functionality
- Update Event model with both has_one_attached :image and image_url virtual attribute
- Create tabbed interface in event forms for upload/URL selection
- Add JavaScript preview functionality for both upload and URL inputs
- Fix promotion code validation issue in tests using distinct() to prevent duplicates
- Update all views to use hybrid display methods prioritizing uploads over URLs
- Update seeds file to use image_url attribute for compatibility
- Ensure backward compatibility with existing events using URL images

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

app/views/pages/home.html.erb

@@ -89,8 +89,12 @@
               <div class="bg-white rounded-2xl shadow-lg hover:shadow-2xl transition-all duration-300 overflow-hidden">
                 <!-- Event Image -->
                 <div class="relative overflow-hidden aspect-[4/3]">
-                  <% if event.image.attached? %>
-                    <%= image_tag event.event_image_variant(:medium), alt: event.name, class: "w-full h-full object-cover group-hover:scale-105 transition-transform duration-300" %>
+                  <% if event.has_image? %>
+                    <% if event.image.attached? %>
+                      <%= image_tag event.event_image_variant(:medium), alt: event.name, class: "w-full h-full object-cover group-hover:scale-105 transition-transform duration-300" %>
+                    <% else %>
+                      <%= image_tag event.image_url, alt: event.name, class: "w-full h-full object-cover group-hover:scale-105 transition-transform duration-300" %>
+                    <% end %>
                   <% else %>
                     <div class="w-full h-full bg-gradient-to-br from-purple-600 to-blue-600 flex items-center justify-center">
                       <i data-lucide="calendar" class="w-16 h-16 text-white"></i>