ci: preserve Changesets prerelease tag

[kauandotnet]

Summary

• read the active Changesets prerelease tag at publish time
• pass that tag explicitly so first-package prereleases update alpha instead of only latest
• fall back to normal Changesets publishing after prerelease mode exits

Verification

• node --check scripts/publish.mjs
• pnpm run check
• pnpm run test
• pnpm run verify:pack