fix: Replace Prawn with Grover for PDF ticket generation

- Replace Prawn PDF generation with Grover (Chrome headless) for better compatibility
- Add HTML-based ticket template with embedded CSS styling
- Implement robust Grover loading with fallback to HTML download
- Add QR code generation methods to Ticket model
- Remove legacy TicketPdfGenerator service and tests
- Update PDF generation in TicketsController with proper error handling

The new implementation provides:
- Better HTML/CSS rendering for ticket layouts
- More reliable PDF generation using Chrome engine
- Fallback mechanism for better user experience
- Cleaner separation of template rendering and PDF conversion

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

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

app/controllers/tickets_controller.rb

@@ -74,18 +74,89 @@ class TicketsController < ApplicationController
       return
     end
 
-    # Generate PDF
-    pdf_content = @ticket.to_pdf
-
-    # Send PDF as download
-    send_data pdf_content,
-              filename: "ticket_#{@ticket.id}_#{@ticket.event.name.parameterize}.pdf",
-              type: "application/pdf",
-              disposition: "attachment"
-  rescue ActiveRecord::RecordNotFound
+    # Generate PDF using Grover
+    begin
+      Rails.logger.info "Starting PDF generation for ticket ID: #{@ticket.id}"
+      
+      # Render the HTML template  
+      html = render_to_string(
+        partial: "tickets/pdf_ticket",
+        layout: false,
+        locals: { ticket: @ticket }
+      )
+      
+      Rails.logger.info "HTML template rendered successfully, length: #{html.length}"
+      
+      # Try to load and use Grover
+      begin
+        Rails.logger.info "Attempting to load Grover gem"
+        
+        # Try different approaches to load grover
+        begin
+          require 'bundler'
+          Bundler.require(:default, Rails.env)
+          Rails.logger.info "Bundler required gems successfully"
+        rescue => bundler_error
+          Rails.logger.warn "Bundler require failed: #{bundler_error.message}"
+        end
+        
+        # Direct path approach using bundle show
+        grover_gem_path = `bundle show grover`.strip
+        grover_path = File.join(grover_gem_path, 'lib', 'grover')
+        
+        if File.exist?(grover_path + '.rb')
+          Rails.logger.info "Loading Grover from direct path: #{grover_path}"
+          require grover_path
+        else
+          Rails.logger.error "Grover not found at path: #{grover_path}"
+          raise LoadError, "Grover gem not available at expected path"
+        end
+        
+        Rails.logger.info "Creating Grover instance with options"
+        grover = Grover.new(html, 
+          format: 'A6',
+          margin: {
+            top: '10mm',
+            bottom: '10mm',
+            left: '10mm',
+            right: '10mm'
+          },
+          prefer_css_page_size: true,
+          emulate_media: 'print',
+          cache: false,
+          launch_args: ['--no-sandbox', '--disable-setuid-sandbox'] # For better compatibility
+        )
+        Rails.logger.info "Grover instance created successfully"
+        
+        pdf_content = grover.to_pdf
+        Rails.logger.info "PDF generated successfully, length: #{pdf_content.length}"
+        
+        # Send PDF as download
+        send_data pdf_content, 
+                  filename: "ticket_#{@ticket.id}_#{@ticket.event.name.parameterize}.pdf",
+                  type: "application/pdf",
+                  disposition: "attachment"
+      rescue LoadError => grover_error
+        Rails.logger.error "Failed to load Grover: #{grover_error.message}"
+        # Fallback: return HTML instead of PDF
+        send_data html,
+                  filename: "ticket_#{@ticket.id}_#{@ticket.event.name.parameterize}.html", 
+                  type: "text/html",
+                  disposition: "attachment"
+      end
+    rescue => e
+      Rails.logger.error "Error generating ticket PDF with Grover:"
+      Rails.logger.error "Message: #{e.message}"
+      Rails.logger.error "Backtrace: #{e.backtrace.join("\n")}"
+      redirect_to dashboard_path, alert: "Erreur lors de la génération du billet"
+    end
+  rescue ActiveRecord::RecordNotFound => e
+    Rails.logger.error "ActiveRecord::RecordNotFound error: #{e.message}"
     redirect_to dashboard_path, alert: "Billet non trouvé"
   rescue => e
-    Rails.logger.error "Error generating ticket PDF: #{e.message}"
+    Rails.logger.error "Unexpected error in download_ticket action:"
+    Rails.logger.error "Message: #{e.message}"
+    Rails.logger.error "Backtrace: #{e.backtrace.join("\n")}"
     redirect_to dashboard_path, alert: "Erreur lors de la génération du billet"
   end