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/mailers/ticket_mailer.rb

@@ -7,11 +7,16 @@ class TicketMailer < ApplicationMailer
 
     # Generate PDF attachments for all tickets
     @tickets.each do |ticket|
-      pdf = ticket.to_pdf
-      attachments["ticket-#{@event.name.parameterize}-#{ticket.qr_code[0..7]}.pdf"] = {
-        mime_type: "application/pdf",
-        content: pdf
-      }
+      begin
+        pdf = ticket.to_pdf
+        attachments["ticket-#{@event.name.parameterize}-#{ticket.qr_code[0..7]}.pdf"] = {
+          mime_type: "application/pdf",
+          content: pdf
+        }
+      rescue StandardError => e
+        Rails.logger.error "Failed to generate PDF for ticket #{ticket.id}: #{e.message}"
+        # Continue without PDF attachment rather than failing the entire email
+      end
     end
 
     mail(
@@ -27,11 +32,16 @@ class TicketMailer < ApplicationMailer
     @event = ticket.event
 
     # Generate PDF attachment
-    pdf = @ticket.to_pdf
-    attachments["ticket-#{@event.name.parameterize}-#{@ticket.qr_code[0..7]}.pdf"] = {
-      mime_type: "application/pdf",
-      content: pdf
-    }
+    begin
+      pdf = @ticket.to_pdf
+      attachments["ticket-#{@event.name.parameterize}-#{@ticket.qr_code[0..7]}.pdf"] = {
+        mime_type: "application/pdf",
+        content: pdf
+      }
+    rescue StandardError => e
+      Rails.logger.error "Failed to generate PDF for ticket #{@ticket.id}: #{e.message}"
+      # Continue without PDF attachment rather than failing the entire email
+    end
 
     mail(
       to: @user.email,