refactor: Replace external QR code dependency with bundled qrcode package

- Install qrcode npm package for proper QR code generation
- Create new Stimulus controller using qrcode library instead of external CDN
- Update ticket show view to use self-contained QR code generation
- Remove dependency on external qrserver.com API
- Generate valid, scannable QR codes client-side

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

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

app/javascript/controllers/index.js

@@ -18,3 +18,6 @@ application.register("ticket-selection", TicketSelectionController);
 
 import HeaderController from "./header_controller";
 application.register("header", HeaderController);
+
+import QrCodeController from "./qr_code_controller";
+application.register("qr-code", QrCodeController);

app/javascript/controllers/qr_code_controller.js

@@ -0,0 +1,56 @@
+// QR Code generator controller using qrcode npm package
+import { Controller } from "@hotwired/stimulus"
+import QRCode from "qrcode"
+
+export default class extends Controller {
+  static values = { data: String }
+  static targets = ["container", "loading"]
+
+  connect() {
+    this.generateQRCode()
+  }
+
+  async generateQRCode() {
+    try {
+      // Hide loading indicator
+      if (this.hasLoadingTarget) {
+        this.loadingTarget.style.display = 'none'
+      }
+
+      // Create canvas element
+      const canvas = document.createElement('canvas')
+      
+      // Generate QR code using qrcode library
+      await QRCode.toCanvas(canvas, this.dataValue, {
+        width: 128,
+        height: 128,
+        margin: 1,
+        color: {
+          dark: '#000000',
+          light: '#FFFFFF'
+        }
+      })
+      
+      // Clear container and add QR code
+      this.containerTarget.innerHTML = ''
+      this.containerTarget.appendChild(canvas)
+      
+      console.log('QR code generated successfully')
+    } catch (error) {
+      console.error('Error generating QR code:', error)
+      this.showFallback()
+    }
+  }
+
+  showFallback() {
+    this.containerTarget.innerHTML = `
+      <div class="w-32 h-32 bg-gray-100 rounded flex items-center justify-center text-gray-500 text-xs border-2 border-dashed border-gray-300">
+        <div class="text-center">
+          <div class="text-lg mb-1">📱</div>
+          <div>QR Code</div>
+          <div class="font-mono text-xs mt-1 break-all px-2">${this.dataValue}</div>
+        </div>
+      </div>
+    `
+  }
+}