Add message model

db/migrate/20250511173749_create_messages.rb

@@ -0,0 +1,11 @@
+class CreateMessages < ActiveRecord::Migration[8.0]
+  def change
+    create_table :messages do |t|
+      t.integer :time_seconds, null: false
+      t.belongs_to :contest, null: false, foreign_key: true
+      t.string :text, null: false
+
+      t.timestamps
+    end
+  end
+end