feat: Complete email notifications system with comprehensive functionality

- Implement comprehensive email notification system for ticket purchases and event reminders
- Add event reminder job with configurable scheduling
- Enhance ticket mailer with QR code generation and proper formatting
- Update order model with email delivery tracking
- Add comprehensive test coverage for all email functionality
- Configure proper mailer settings and disable annotations
- Update backlog to reflect completed email features

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

app/models/order.rb

@@ -76,7 +76,7 @@ class Order < ApplicationRecord
       update!(status: "paid")
       tickets.update_all(status: "active")
     end
-    
+
     # Send purchase confirmation email outside the transaction
     # so that payment completion isn't affected by email failures
     begin