feat: Implement event image upload system for promoters

- Add Active Storage migrations for file attachments
- Update Event model to handle image uploads with validation
- Replace image URL fields with file upload in forms
- Add client-side image preview with validation
- Update all views to display uploaded images properly
- Fix JSON serialization to prevent stack overflow in API
- Add custom image validation methods for format and size
- Include image processing variants for different display sizes
- Fix promotion code test infrastructure and Stripe configuration

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

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

app/models/event.rb

@@ -22,7 +22,9 @@ class Event < ApplicationRecord
   has_many :tickets, through: :ticket_types
   has_many :orders
   has_many :promotion_codes
+  has_one_attached :image
 
+  
   # === Callbacks ===
   before_validation :geocode_address, if: :should_geocode_address?
 
@@ -32,7 +34,8 @@ class Event < ApplicationRecord
   validates :slug, presence: true, length: { minimum: 3, maximum: 100 }
   validates :description, presence: true, length: { minimum: 10, maximum: 2000 }
   validates :state, presence: true, inclusion: { in: states.keys }
-  validates :image, length: { maximum: 500 } # URL or path to image
+  validate :image_format, if: -> { image.attached? }
+  validate :image_size, if: -> { image.attached? }
 
   # Venue information
   validates :venue_name, presence: true, length: { maximum: 100 }
@@ -58,6 +61,20 @@ class Event < ApplicationRecord
 
   # === Instance Methods ===
 
+  # Get image variants for different display sizes
+  def event_image_variant(size = :medium)
+    case size
+    when :large
+      image.variant(resize_to_limit: [1200, 630])
+    when :medium
+      image.variant(resize_to_limit: [800, 450])
+    when :small
+      image.variant(resize_to_limit: [400, 225])
+    else
+      image
+    end
+  end
+
   # Check if coordinates were successfully geocoded or are fallback coordinates
   def geocoding_successful?
     coordinates_look_valid?
@@ -131,6 +148,25 @@ class Event < ApplicationRecord
     nil
   end
 
+  # Validate image format
+  def image_format
+    return unless image.attached?
+
+    allowed_types = %w[image/jpeg image/jpg image/png image/webp]
+    unless allowed_types.include?(image.content_type)
+      errors.add(:image, "doit être au format JPG, PNG ou WebP")
+    end
+  end
+
+  # Validate image size
+  def image_size
+    return unless image.attached?
+
+    if image.byte_size > 5.megabytes
+      errors.add(:image, "doit faire moins de 5MB")
+    end
+  end
+
   private
 
   # Determine if we should perform server-side geocoding