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/javascript/controllers/event_form_controller.js

@@ -687,8 +687,8 @@ export default class extends Controller {
     // Show preview
     const reader = new FileReader()
     reader.onload = (e) => {
-      const previewContainer = document.getElementById('image-preview')
-      const previewImg = document.getElementById('preview-img')
+      const previewContainer = document.getElementById('upload-preview')
+      const previewImg = document.getElementById('upload-preview-img')
 
       if (previewContainer && previewImg) {
         previewImg.src = e.target.result
@@ -697,4 +697,54 @@ export default class extends Controller {
     }
     reader.readAsDataURL(file)
   }
+
+  // Preview image from URL
+  previewImageUrl(event) {
+    const url = event.target.value.trim()
+    const previewContainer = document.getElementById('url-preview')
+    const previewImg = document.getElementById('url-preview-img')
+
+    if (!url) {
+      if (previewContainer) {
+        previewContainer.classList.add('hidden')
+      }
+      return
+    }
+
+    // Basic URL validation
+    if (!this.isValidImageUrl(url)) {
+      if (previewContainer) {
+        previewContainer.classList.add('hidden')
+      }
+      return
+    }
+
+    // Show preview with error handling
+    if (previewImg) {
+      previewImg.onload = () => {
+        if (previewContainer) {
+          previewContainer.classList.remove('hidden')
+        }
+      }
+
+      previewImg.onerror = () => {
+        if (previewContainer) {
+          previewContainer.classList.add('hidden')
+        }
+      }
+
+      previewImg.src = url
+    }
+  }
+
+  // Validate image URL format
+  isValidImageUrl(url) {
+    try {
+      new URL(url)
+      // Check if it looks like an image URL
+      return /\.(jpg|jpeg|png|gif|webp)(\?.*)?$/i.test(url)
+    } catch {
+      return false
+    }
+  }
 }