npm install -g n && n <version> keeps failing in the worker base image
(serenity-js/playwright:v1.58.1-noble): n is not resolvable on PATH and
its package-bin path 404s too, indicating a global-prefix / shebang mismatch
in the image that the removed buildx cache had been masking.
Replace the n-based node install with the official Node linux-x64 tarball extracted into /usr/local. No dependency on npm global bin or n's bash shebang. Includes a one-line env diagnostic and node/npm version checks so a future regression fails loudly with context.