ci(website): reinstall platform dependencies from clean tree

[hongjr03]

Summary

• Reinstall website dependencies from a clean node_modules tree in docs preview and deployment workflows.
• Keep the existing lockfile validation while ensuring the runner resolves platform-specific native optional dependencies.

Root cause

The docs job failed because npm did not install @rolldown/binding-linux-x64-gnu. npm can prune platform-specific optional dependencies when node_modules already exists, so the existing npm ci followed by npm install --no-save did not repair the dependency tree.

Validation

• actionlint .github/workflows/docs-preview.yml .github/workflows/deploy-docs.yml (no YAML errors; existing ShellCheck warnings remain in deploy-docs.yml).
• npm ci --ignore-scripts in website.
• npm --prefix playground run build:embed passed.
• Full npm run build reached the expected WASM asset check but could not continue locally because CI-generated website/playground/public/wasm/vide-lsp.js was not present.