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/services/ticket_pdf_generator.rb

@@ -74,18 +74,21 @@ class TicketPdfGenerator
         raise "Ticket QR code is missing"
       end
 
-      qr_code_data = {
-        ticket_id: ticket.id,
-        qr_code: ticket.qr_code,
-        event_id: ticket.event&.id,
-        user_id: ticket.user&.id
-      }.compact.to_json
+      # Build QR code data with safe association loading
+      qr_code_data = build_qr_code_data(ticket)
 
       # Validate QR code data before creating QR code
       if qr_code_data.blank? || qr_code_data == "{}"
+        Rails.logger.error "QR code data is empty: ticket_id=#{ticket.id}, qr_code=#{ticket.qr_code}, event_id=#{ticket.ticket_type&.event_id}, user_id=#{ticket.order&.user_id}"
         raise "QR code data is empty or invalid"
       end
 
+      # Ensure qr_code_data is a proper string for QR code generation
+      unless qr_code_data.is_a?(String) && qr_code_data.length > 2
+        Rails.logger.error "QR code data is not a valid string: #{qr_code_data.inspect} (class: #{qr_code_data.class})"
+        raise "QR code data must be a valid string"
+      end
+
       qrcode = RQRCode::QRCode.new(qr_code_data)
       pdf.print_qr_code(qrcode, extent: 120, align: :center)
 
@@ -110,4 +113,36 @@ class TicketPdfGenerator
       pdf.text "Generated on #{Time.current.strftime('%B %d, %Y at %I:%M %p')}", align: :center
     end.render
   end
+
+  private
+
+  def build_qr_code_data(ticket)
+    # Try multiple approaches to get valid QR code data
+    begin
+      # Primary approach: full JSON with all data
+      data = {
+        ticket_id: ticket.id,
+        qr_code: ticket.qr_code,
+        event_id: ticket.ticket_type&.event_id,
+        user_id: ticket.order&.user_id
+      }.compact
+
+      # Ensure we have the minimum required data
+      if data[:ticket_id] && data[:qr_code]
+        return data.to_json
+      end
+    rescue StandardError => e
+      Rails.logger.warn "Failed to build complex QR data: #{e.message}"
+    end
+
+    # Fallback approach: just use the ticket's QR code string
+    begin
+      return ticket.qr_code.to_s if ticket.qr_code.present?
+    rescue StandardError => e
+      Rails.logger.warn "Failed to use ticket QR code: #{e.message}"
+    end
+
+    # Final fallback: simple ticket identifier
+    "TICKET-#{ticket.id}"
+  end
 end