Track and handle bounced customer and notification emails

The platform now tracks bounced email addresses for both store notifications and customer profiles, exposing new fields (email_bounced_at and email_bounce_reason) via the API. When an email bounces, the system automatically skips it for store alerts and triggers domain events (recipient.bounced, recipient.bounce_cleared, and recipient.deleted). Updating or replacing an affected email address automatically clears its bounce state so normal messaging can resume.