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>

package.json

@@ -11,6 +11,7 @@
     "@hotwired/turbo-rails": "^8.0.13",
     "@radix-ui/react-slot": "^1.2.3",
     "lucide": "^0.542.0",
+    "qrcode": "^1.5.4",
     "react": "^18.3.1",
     "react-dom": "^18.3.1"
   },