fix: Resolve QR code generation errors in checkout email notifications

This fixes the 'data must be a String, QRSegment, or an Array' error that was
preventing checkout completion.

Changes:
- Move email sending outside payment transaction to avoid rollback on email failure
- Add error handling around PDF generation in mailers
- Improve QR code data building with multiple fallback strategies
- Use direct foreign key access instead of through associations for reliability
- Add comprehensive logging for debugging QR code issues
- Ensure checkout succeeds even if email/PDF generation fails

The payment process will now complete successfully regardless of email issues,
while still attempting to send confirmation emails with PDF attachments.

app/models/order.rb

@@ -75,9 +75,16 @@ class Order < ApplicationRecord
     transaction do
       update!(status: "paid")
       tickets.update_all(status: "active")
-      
-      # Send purchase confirmation email
+    end
+    
+    # Send purchase confirmation email outside the transaction
+    # so that payment completion isn't affected by email failures
+    begin
       TicketMailer.purchase_confirmation_order(self).deliver_now
+    rescue StandardError => e
+      Rails.logger.error "Failed to send purchase confirmation email for order #{id}: #{e.message}"
+      Rails.logger.error e.backtrace.join("\n")
+      # Don't re-raise the error - payment should still succeed
     end
   end