[docs] Make website dependency installs reproducible

[hutiefang76]

Purpose

Linked issue: close #3502

Make the website dependency install reproducible. The website currently ignores lockfiles and the docs check workflow uses npm install, so each run can re-resolve Docusaurus package ranges differently.

Brief change log

• Stop ignoring website npm/pnpm lockfiles.
• Commit website/package-lock.json generated from the current website/package.json.
• Use npm ci in the documentation check workflow so CI installs from the committed lockfile instead of resolving a fresh tree.

Tests

• npm ci --no-audit --no-fund
• ./build_versioned_docs.sh && ./setup_blog.sh && npm run build -- --no-minify
• npm run typecheck

API and Format

No API or storage format changes.

Documentation

No user-facing documentation changes.

Generative AI disclosure

• No generative AI tools used
• Yes: OpenAI Codex assisted with preparing the patch and running local verification.