npm: Use workspaces to simplify `hugo mod npm pack`

npm: Use workspaces to simplify `hugo mod npm pack`

Rewrite `hugo mod npm pack` to use npm workspaces. Module deps are now
written to packages/hugoautogen/package.json and the root package.json
gets a "workspaces" reference. A hugo_packagemeta.json sidecar stores a
hash of all input package files so regular commands can warn when npm
deps are out of sync.

Other changes:
- Workspace glob patterns (*, **, {a,b}) are resolved via gobwas/glob.
- Workspaces defined in package.hugo.json are supported.
- package.hugo.json is only recognised at module roots, not in workspaces.
- When package.hugo.json exists, package.json is not mounted or vendored.
- packages/hugoautogen is not mounted or vendored from dependencies.
- Add usePackageJSON import option (auto/always/never) to control whether
  a module's npm deps are included. "auto" checks for Hugo config files
  or package.hugo.json.
- The staleness check is skipped when running `hugo mod npm pack` itself.

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>