upgrade-frontend-deps

Upgrade the Next.js frontend's pnpm dependencies to their latest versions in verified waves. Inventories with pnpm outdated, removes verified-unused deps, batches safe minor/patch bumps, handles the @langchain/react + langgraph-sdk lockstep pair, takes majors one commit at a time with registry peer-dep checks, gates every wave on type-check + lint + unit tests + build + an agent-browser check against baseline…