feat(vault): real QR code generation for WiFi entries

Replace placeholder WiFi string display with actual QR code rendered
on canvas via 'qrcode' library. Dialog now shows scannable QR image
with copy-image and download-PNG buttons.

package.json

@@ -20,6 +20,7 @@
     "next": "16.1.6",
     "next-auth": "^4.24.13",
     "next-themes": "^0.4.6",
+    "qrcode": "^1.5.4",
     "radix-ui": "^1.4.3",
     "react": "19.2.3",
     "react-dom": "19.2.3",
@@ -32,6 +33,7 @@
     "@tailwindcss/postcss": "^4",
     "@types/jszip": "^3.4.0",
     "@types/node": "^20",
+    "@types/qrcode": "^1.5.6",
     "@types/react": "^19",
     "@types/react-dom": "^19",
     "@types/uuid": "^10.0.0",