Community node installs now accept npm dist-tags

When installing a community node using an npm dist-tag — for example n8n-nodes-imap@beta — n8n was rejecting the input with "Invalid version: beta" because its validation logic only recognized strict semver strings. Dist-tags like beta, next, and latest are standard npm version specifiers, but n8n's version check treated everything after the @ symbol as a semver string and threw an error.

The fix adds a helper that recognizes valid npm dist-tags alongside existing semver validation. When a dist-tag is used, n8n resolves it to the underlying semver version via npm before proceeding — keeping the stored version precise while supporting the more ergonomic install syntax. The upstream restriction on unsafe specifiers (git URLs, tarball URLs, semver ranges) remains in place.

This is a narrow but meaningful quality-of-life fix for anyone who manages n8n nodes using the same npm workflow they use elsewhere.