Add rake task to backfill item_tags.position for existing rows

Assigns sequential position values per shop, ordered by created_at,
starting from current max+1, skipping callbacks/validations.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: dadachi

lib/tasks/item_tags.rake

@@ -0,0 +1,18 @@
+namespace :item_tags do
+  desc "Backfill position for existing item_tags grouped by shop, ordered by created_at"
+  task backfill_position: :environment do
+    ActsAsTenant.without_tenant do
+      Shop.find_each do |shop|
+        next_position = (shop.item_tags.maximum(:position) || 0) + 1
+
+        shop.item_tags.where(position: nil).order(:created_at, :id).each do |item_tag|
+          item_tag.update_columns(position: next_position)
+          puts "Shop #{shop.id} - ItemTag #{item_tag.id}: position=#{next_position}"
+          next_position += 1
+        end
+      end
+    end
+
+    puts "Done."
+  end
+end