Offline participation form: ask for missing/remaining pieces

db/migrate/20251108082730_add_missing_pieces_to_offline.rb

@@ -0,0 +1,5 @@
+class AddMissingPiecesToOffline < ActiveRecord::Migration[8.0]
+  def change
+    add_column :offlines, :missing_pieces, :integer
+  end
+end

db/migrate/20251108082751_add_remaining_pieces_to_offline.rb

@@ -0,0 +1,5 @@
+class AddRemainingPiecesToOffline < ActiveRecord::Migration[8.0]
+  def change
+    add_column :offlines, :remaining_pieces, :integer
+  end
+end