fix: switch CI to pnpm to resolve native binding failure on Linux runners

[Copilot]

npm ci has a known bug (npm/cli#4828) where platform-specific optional dependencies aren't installed correctly — causing @tailwindcss/oxide to fail with "Cannot find native binding" on Linux CI runners when package-lock.json was generated on macOS.

The repo already ships a pnpm-lock.yaml, so switching to pnpm is the natural fix; pnpm resolves platform-specific optionals correctly.

Changes to .github/workflows/astro.yml

• Package manager detection — pnpm-lock.yaml is now checked first; each branch emits a lockfile output so downstream steps stay generic
• pnpm setup — adds pnpm/action-setup@v4 (pinned to v9, matching lockfileVersion: '9.0' in the lockfile) before setup-node so caching works
• Dynamic cache-dependency-path — uses ${{ steps.detect-package-manager.outputs.lockfile }} instead of the hardcoded package-lock.json
• Node.js 18 → 20 — 18 is EOL

- name: Install pnpm
  if: steps.detect-package-manager.outputs.manager == 'pnpm'
  uses: pnpm/action-setup@v4
  with:
    version: 9
- name: Setup Node
  uses: actions/setup-node@v6
  with:
    node-version: "20"
    cache: ${{ steps.detect-package-manager.outputs.manager }}
    cache-dependency-path: ${{ env.BUILD_PATH }}/${{ steps.detect-package-manager.outputs.lockfile }}

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[Copilot]

Pull request overview

This PR updates the GitHub Pages “Astro” workflow to prefer pnpm in CI (to avoid platform-specific optional dependency issues seen with npm ci), while also modernizing the Node runtime and making dependency caching lockfile-aware.

Changes:

• Prefer pnpm-lock.yaml during package-manager detection and expose a lockfile output for downstream steps.
• Add pnpm/action-setup@v4 (pnpm v9) and switch Node.js from 18 to 20.
• Make actions/setup-node caching use a dynamic cache-dependency-path based on the detected lockfile.

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[Copilot]

The lockfile detection is hard-coded to ${{ github.workspace }} and ignores env.BUILD_PATH. If BUILD_PATH is set to a subfolder (as the workflow hints), this step will fail to detect the correct manager/lockfile even though later steps run from working-directory: ${{ env.BUILD_PATH }}. Consider checking for lockfiles under ${{ github.workspace }}/${{ env.BUILD_PATH }} (or cd into BUILD_PATH within this step) so detection stays consistent with the rest of the workflow.

Suggested change

	if [ -f "${{ github.workspace }}/pnpm-lock.yaml" ]; then
	echo "manager=pnpm" >> $GITHUB_OUTPUT
	echo "command=install" >> $GITHUB_OUTPUT
	echo "runner=pnpm" >> $GITHUB_OUTPUT
	echo "lockfile=pnpm-lock.yaml" >> $GITHUB_OUTPUT
	exit 0
	elif [ -f "${{ github.workspace }}/yarn.lock" ]; then
	echo "manager=yarn" >> $GITHUB_OUTPUT
	echo "command=install" >> $GITHUB_OUTPUT
	echo "runner=yarn" >> $GITHUB_OUTPUT
	echo "lockfile=yarn.lock" >> $GITHUB_OUTPUT
	exit 0
	elif [ -f "${{ github.workspace }}/package.json" ]; then
	if [ -f "${{ github.workspace }}/${{ env.BUILD_PATH }}/pnpm-lock.yaml" ]; then
	echo "manager=pnpm" >> $GITHUB_OUTPUT
	echo "command=install" >> $GITHUB_OUTPUT
	echo "runner=pnpm" >> $GITHUB_OUTPUT
	echo "lockfile=pnpm-lock.yaml" >> $GITHUB_OUTPUT
	exit 0
	elif [ -f "${{ github.workspace }}/${{ env.BUILD_PATH }}/yarn.lock" ]; then
	echo "manager=yarn" >> $GITHUB_OUTPUT
	echo "command=install" >> $GITHUB_OUTPUT
	echo "runner=yarn" >> $GITHUB_OUTPUT
	echo "lockfile=yarn.lock" >> $GITHUB_OUTPUT
	exit 0
	elif [ -f "${{ github.workspace }}/${{ env.BUILD_PATH }}/package.json" ]; then

[Copilot]

For CI determinism, pnpm install without a frozen/immutable flag can silently resolve and update the lockfile, which can make builds succeed despite lockfile drift. Consider setting the pnpm command output to use --frozen-lockfile (and similarly for yarn if you want parity with npm ci) so the workflow fails when the lockfile and manifest are out of sync.

Suggested change

	echo "command=install" >> $GITHUB_OUTPUT
	echo "runner=pnpm" >> $GITHUB_OUTPUT
	echo "lockfile=pnpm-lock.yaml" >> $GITHUB_OUTPUT
	exit 0
	elif [ -f "${{ github.workspace }}/yarn.lock" ]; then
	echo "manager=yarn" >> $GITHUB_OUTPUT
	echo "command=install" >> $GITHUB_OUTPUT
	echo "command=install --frozen-lockfile" >> $GITHUB_OUTPUT
	echo "runner=pnpm" >> $GITHUB_OUTPUT
	echo "lockfile=pnpm-lock.yaml" >> $GITHUB_OUTPUT
	exit 0
	elif [ -f "${{ github.workspace }}/yarn.lock" ]; then
	echo "manager=yarn" >> $GITHUB_OUTPUT
	echo "command=install --frozen-lockfile" >> $GITHUB_OUTPUT