Offline participation: implement completed puzzle methods

db/migrate/20251031095604_add_completed_to_offline.rb

@@ -0,0 +1,5 @@
+class AddCompletedToOffline < ActiveRecord::Migration[8.0]
+  def change
+    add_column :offlines, :completed, :boolean
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.0].define(version: 2025_10_30_094151) do
+ActiveRecord::Schema[8.0].define(version: 2025_10_31_095604) do
   create_table "active_storage_attachments", force: :cascade do |t|
     t.string "name", null: false
     t.string "record_type", null: false
@@ -133,6 +133,7 @@ ActiveRecord::Schema[8.0].define(version: 2025_10_30_094151) do
     t.datetime "start_time", null: false
     t.datetime "end_time"
     t.string "name", null: false
+    t.boolean "completed"
     t.index ["contest_id"], name: "index_offlines_on_contest_id"
   end