docs: align build requirements with CI

[Optic00]

Summary

• Use npm ci for manual and troubleshooting builds so the lockfile remains authoritative.
• Document Go 1.27.0, Node.js 24.18.0, and npm 11.16.0 as the exact required versions.
• Keep troubleshooting cleanup limited to node_modules and verify the npm cache before reinstalling.

Verification

The documented versions were checked against go.mod, .nvmrc, and frontend/package.json. The install command matches the Makefile and GitHub workflows.

[stefan-ernst]

thanks! moving this in