Remove pnpm run build (and pnpm run test) calls from publish-release.ts
and prerelease.ts so that repository build code never executes with
NPM_TOKEN in the environment. The CI build job (contents: read, no
secrets) now handles all building and testing, uploading pre-built
artifacts for the publish job to consume.
For prerelease: extract version bumping into a new bump-prerelease.ts
script that runs in the build job before the build step, ensuring the
built artifacts contain the correct canary version numbers.
Also fix prerelease build job to use persist-credentials: false,
matching the publish-release build job pattern.