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/controllers/parties_controller.rb

@@ -1,4 +1,4 @@
-class EventsController < ApplicationController
+class PartiesController < ApplicationController
   # Display all events
   def index
     @parties = Party.includes(:user).upcoming.page(params[:page]).per(12)
@@ -6,5 +6,6 @@ class EventsController < ApplicationController
 
   # Display desired event
   def show
+    @party = Party.find(params[:id])
   end
 end