fix(docs): upgrade vulnerable dependencies

[fewensa]

Summary

• remove the deprecated polyfill.io script from the MkDocs JavaScript bundle
• refresh the Poetry lockfile so Dependabot-alerted packages resolve to patched versions
• add explicit least-privilege GITHUB_TOKEN permissions to the preview/staging workflows flagged by CodeQL

Security notes

• GitHub Dependabot alerts were open for vulnerable pip packages in poetry.lock
• Patched versions now include GitPython 3.1.50, urllib3 2.7.0, requests 2.34.2, Jinja2 3.1.6, Markdown 3.10.2, Pygments 2.20.0, pymdown-extensions 10.21.3, and idna 3.18
• The published site was loading https://polyfill.io/v3/polyfill.min.js?features=es6; this PR removes that external script
• Code scanning alerts actions/missing-workflow-permissions for deploy-dev.yml and deploy-stg.yml are addressed with explicit permissions blocks

Validation

• uvx --from poetry==1.8.3 poetry check
• uvx --from poetry==1.8.3 poetry install --no-root
• uvx --from poetry==1.8.3 poetry run mkdocs build
• uvx pip-audit -r exported-requirements.txt: No known vulnerabilities found
• rg polyfill.io against source and generated site returned no matches
• git diff --check

[github-actions]

• comment: 86168ee
  preview: https://darwinia-docs-lw6zzuad9-itering.vercel.app https://darwinia-docs-dev.vercel.app
• comment: 244fa5f
  preview: https://darwinia-docs-rel1f30j8-itering.vercel.app https://darwinia-docs-dev.vercel.app
• comment: f084c17
  preview: https://darwinia-docs-fedw5kbqw-itering.vercel.app https://darwinia-docs-dev.vercel.app

[chatgpt-codex-connector]

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