Support npm package sources in hunk extension install #1115

What do you want to change?

Support npm package sources in hunk extension install, alongside the existing Git and local sources.

hunk extension install npm:@brettinternet/hunk-guide
hunk extension install npm:@brettinternet/hunk-guide@1.2.0

This should support scoped packages, versions, ranges, and tags; discover entries from hunk.extensions; and integrate with hunk extension list, update, and remove. The install record should include the requested source and resolved package version.

Why?

npm packages allow extensions to have independent releases, immutable versions, provenance, and normal dependency distribution. They also let a repository contain several extensions while users install only the one they want.

Git sources would remain useful for extension bundles and unpublished extensions.

How? (optional)

Install the resolved package into Hunk's managed extensions directory and use its existing manifest discovery. Keep the current confirmation and trust behavior for managed installs.