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.

config/routes.rb

@@ -12,9 +12,9 @@ Rails.application.routes.draw do
   # Defines the root path route ("/")
   root "pages#home"
 
-  # Events page
-  get "events", to: "events#index"
-  get "events/:id", to: "events#show"
+  # parties page
+  get "parties",              to: "parties#index",  as: "parties"
+  get "parties/:slug.:id",        to: "parties#show",   as: "party"
 
   # Routes for devise authentication Gem
   # Bind devise to user