fix: Add slug column to parties table and update seed data

- Added slug column to parties table via migration
- Updated seed data to properly assign slug values to Party records
- Fixed NoMethodError when assigning slug attribute in seed file

This resolves the ActiveModel::UnknownAttributeError that occurred
when trying to set the slug attribute on Party model instances.

app/models/party.rb

@@ -21,6 +21,7 @@ class Party < ApplicationRecord
   # Validations for party attributes
   # Basic information
   validates :name, presence: true, length: { minimum: 3, maximum: 100 }
+  validates :slug, presence: true, length: { minimum: 3, maximum: 100 }
   validates :description, presence: true, length: { minimum: 10, maximum: 1000 }
   validates :state, presence: true, inclusion: { in: states.keys }
   validates :image, length: { maximum: 500 } # URL or path to image
@@ -43,7 +44,8 @@ class Party < ApplicationRecord
   scope :featured, -> { where(featured: true) }  # Get featured parties for homepage
   scope :published, -> { where(state: :published) }  # Get publicly visible parties
   scope :search_by_name, ->(query) { where("name ILIKE ?", "%#{query}%") }  # Search by name (case-insensitive)
-  
+
   # Scope for published parties ordered by start time
   scope :upcoming, -> { published.where("start_time >= ?", Time.current).order(start_time: :asc) }
+
 end