feat: Merge PDF ticket generation functionality from feat/pdf-ticket branch

- Add TicketPdfGenerator service for creating PDF tickets with QR codes
- Implement download_ticket action in TicketsController
- Update ticket routes to support both ID and QR code access
- Add to_pdf method to Ticket model using TicketPdfGenerator
- Resolve conflicts between email notifications and PDF ticket features
- Maintain backward compatibility with existing QR code routes

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

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

app/views/tickets/show.html.erb

@@ -159,7 +159,7 @@
             <% end %>
 
             <% if @ticket.status == 'active' %>
-              <%= link_to ticket_download_path(@ticket.qr_code),
+              <%= link_to download_ticket_path(@ticket.id),
                           class: "flex-1 bg-gradient-to-r from-purple-600 to-indigo-600 hover:from-purple-700 hover:to-indigo-700 text-white font-medium py-3 px-6 rounded-xl shadow-sm transition-all duration-200 focus:outline-none focus:ring-2 focus:ring-purple-500 focus:ring-offset-2 transform hover:-translate-y-0.5 text-center" do %>
                 <svg class="w-4 h-4 inline-block mr-2" fill="none" stroke="currentColor" viewBox="0 0 24 24">
                   <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M12 10v6m0 0l-3-3m3 3l3-3m2 8H7a2 2 0 01-2-2V5a2 2 0 012-2h5.586a1 1 0 01.707.293l5.414 5.414a1 1 0 01.293.707V19a2 2 0 01-2 2z"/>