ALTER TABLE users
  ADD COLUMN stripe_customer_id VARCHAR(255) NULL,
  ADD COLUMN stripe_subscription_id VARCHAR(255) NULL,
  ADD COLUMN subscription_plan ENUM('standard','standard_plus','premium','premium_plus') NULL,
  ADD COLUMN subscription_status VARCHAR(50) NULL DEFAULT 'inactive',
  ADD COLUMN trial_ends_at DATETIME NULL,
  ADD COLUMN current_period_end DATETIME NULL;
