Fix dependency audit issues and legacy tap support

[RandomPerson208]

Summary

• Remove the runtime fastly dependency by switching the helper to built-in fetch and tightening error handling.
• Refresh the toolchain and lockfile for newer tap, copy-webpack-plugin, canvas, webpack-dev-middleware, plotly.js, react-plotly.js, and webpack-bundle-analyzer releases, plus targeted overrides for Scratch GUI transitive packages.
• Keep the legacy tap tests green by removing deprecated tearDown hooks and replacing old assertion calls with t.same.
• Update the webpack config and README to match the newer dependency/tooling shape.

Files touched

• README.md
• bin/configure-fastly.js
• bin/lib/fastly-extended.js
• package.json
• package-lock.json
• test/unit-legacy/redux/comments-test.js
• test/unit-legacy/redux/preview-test.js
• test/unit/lib/fastly-extended.test.js
• webpack.config.js

Validation

• npm run test
• npm audit --omit=dev -> 0 vulnerabilities
• Full npm audit still reports 32 dev-only issues in upstream package trees that are not yet directly fixable in this branch.

Issues

• Fixes Audit npm dependencies #564

[RandomPerson208]

I have read the CLA Document and I hereby sign the CLA