refactor(webrtc): migrate troubleshooting app to Web SDK NG 4.24.6

[sunshinexcode]

Summary

Upgrade Agora WebRTC Troubleshooting from Web SDK 3.x to Web SDK NG 4.24.6 and update the related build and token workflows.

Changes

• Migrate stream-based RTC APIs to Web SDK NG track-based APIs.
• Update publishing, subscribing, playback, cleanup, and remote statistics handling.
• Generate RTC tokens through the global Toolbox service when an App Certificate is configured.
• Join with a null token when the App Certificate is empty.
• Remove the default App ID and load credentials from VUE_APP_* environment variables.
• Fix the 240p_1 video profile and update the TCP 443 proxy mode.
• Upgrade Vue CLI and ESLint dependencies for newer Node.js compatibility.
• Standardize dependency management on npm and remove yarn.lock.
• Update README instructions and Web SDK NG API references.

Security

VUE_APP_* values are embedded in browser JavaScript. App Certificate configuration is intended for local troubleshooting only and must not be used in a deployed production build.

Verification

• npm install
• npm run lint
• npm run build
• Started the development server and verified that the page loads with Web SDK NG 4.24.6.