add migration to remove standard series from db

db/data/20251215200000_remove_standard_character_series.rb

@@ -0,0 +1,41 @@
+# frozen_string_literal: true
+
+class RemoveStandardCharacterSeries < ActiveRecord::Migration[8.0]
+  def up
+    # Find and delete the 'standard' series
+    standard = CharacterSeries.find_by(slug: 'standard')
+
+    if standard
+      # Delete any memberships to 'standard' first
+      membership_count = CharacterSeriesMembership.where(character_series: standard).delete_all
+      puts "Deleted #{membership_count} memberships to 'standard' series"
+
+      # Delete the series record
+      standard.destroy!
+      puts "Deleted 'standard' character series"
+    else
+      puts "'standard' character series not found, skipping"
+    end
+
+    # Update order values for remaining series (shift down by 1)
+    CharacterSeries.where('"order" > 0').find_each do |cs|
+      cs.update!(order: cs.order - 1)
+    end
+    puts "Updated order values for remaining series"
+  end
+
+  def down
+    # Re-create the standard series and shift orders back up
+    CharacterSeries.find_each do |cs|
+      cs.update!(order: cs.order + 1)
+    end
+
+    CharacterSeries.create!(
+      order: 0,
+      slug: 'standard',
+      name_en: 'Standard',
+      name_jp: 'スタンダード'
+    )
+    puts "Re-created 'standard' character series"
+  end
+end