Fix pnpm setup in publish workflow

[thebuilder]

Summary

• remove pnpm caching from actions/setup-node
• enable the Corepack shim before invoking pnpm
• run the repository-pinned package manager as plain pnpm in GitHub Actions

Root cause

actions/setup-node initializes its package-manager cache during the setup step. With cache: pnpm, it attempted to execute pnpm before the following install step had run corepack enable, causing the release workflow to fail with Unable to locate executable file: pnpm.

Impact

The publish workflow can now complete Node setup and install the backoffice dependencies using the pnpm version pinned by the repository's packageManager field. The optional setup-node dependency cache is disabled.

Verification

• parsed the workflow as valid YAML
• verified corepack enable exposes plain pnpm
• verified the final workflow diff is limited to the setup and install commands
• confirmed the original failure in GitHub Actions run 29637969266