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>

db/schema.rb

@@ -56,6 +56,7 @@ ActiveRecord::Schema[8.0].define(version: 2025_09_29_222616) do
     t.boolean "allow_booking_during_event", default: false, null: false
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
+    t.string "image_url"
     t.index ["featured"], name: "index_events_on_featured"
     t.index ["latitude", "longitude"], name: "index_events_on_latitude_and_longitude"
     t.index ["state"], name: "index_events_on_state"