-- Add plugin column to subscriptions (allows per-plugin subscriptions)
ALTER TABLE subscriptions ADD COLUMN plugin VARCHAR(30) DEFAULT 'translate';

-- Drop old unique constraint on user_id alone
ALTER TABLE subscriptions DROP CONSTRAINT IF EXISTS subscriptions_user_id_key;

-- Add new composite unique constraint on (user_id, plugin)
ALTER TABLE subscriptions ADD CONSTRAINT subscriptions_user_id_plugin_key UNIQUE (user_id, plugin);
