[web] Generate QR codes on webUI client instead of remote API

[LJspice]

Adding one client-executed QR-code generator script to replace the api.qrserver.com call. It didn't seem great or necessary to send thread.pskd out in the existing implementation.

Demo

[gemini-code-assist]

Code Review

This pull request replaces the external QR code generation API with a local generator using the qrcode-generator library. This change includes updating the project dependencies in package.json, package-lock.json, CMakeLists.txt, and index.html, and refactoring app.js to handle QR code generation locally within a try-catch block. The review feedback suggests adding defensive checks to ensure that response.data.eui64 and $scope.thread.pskd are defined before generating the QR code, preventing literal 'undefined' or 'null' values from being encoded.