npm documents trusted publishing for `npm publish` run inside a package
directory; publishing a pre-packed .tgz path is undocumented there and is a
plausible cause of the OIDC failures on the last release attempts.

pack.mjs gains --stage-out, which keeps the verified staging tree, and the
release workflow publishes from it. The tree is the exact one the tarball is
packed from, so every gate still describes what ships.

Also drop --provenance: with trusted publishing npm generates provenance
automatically for a public package from a public repository, so the flag is
redundant and one more thing that can disagree with the OIDC path.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>