Drain dserve Dependabot alerts

[lancewillett]

Summary

• update vulnerable direct dependencies and Yarn resolutions so yarn audit reports zero vulnerabilities across all severities
• remove forever-monitor and replace it with a small child-process restart loop, avoiding its unpatched watcher dependency tree
• remove useragent and use a small browser user-agent check to avoid its unpatched dependency tree

This should supersede the stale Dependabot PR queue once merged.

Testing

• yarn install --frozen-lockfile
• yarn run build-ts
• yarn test --runInBand
• yarn run audit:critical
• yarn audit --json | jq -r 'select(.type=="auditSummary") | .data.vulnerabilities' -> all zero\n- git diff --check\n\nNote: Yarn still prints resolution compatibility warnings for forced patched transitive versions. yarn install exits successfully.