fix: guard release tarball rename against same-file mv

[narthur]

What

Guard the mv in the release workflow's pack step so it doesn't try to move the tarball onto itself.

Why it failed

Third time's the charm. The last run got all the way through semver-bootstrap, install, build, and pack — then died on:

mv: 'expost-1.0.0.tgz' and 'expost-1.0.0.tgz' are the same file

pnpm pack names the tarball from package.json's version (1.0.0), and the release tag resolved to v1.0.0, so the rename-to-tag mv had identical source and dest → error → no release.

Fix

Only rename when the packed name and the tag-derived name actually differ (they diverge once tags advance past the static package.json version):

src=$(ls expost-*.tgz)
dest="expost-${VERSION#v}.tgz"
[ "$src" = "$dest" ] || mv "$src" "$dest"

Verified both branches locally (same-name → skip; 1.0.0 pack + v1.1.0 tag → renames to expost-1.1.0.tgz).

Result

Merging cuts v1.0.0 with expost-1.0.0.tgz attached (every prior step already passed on the last run), unblocking beeminder/blog#762.

🤖 Generated with Claude Code