ci: cache npm publish dependencies

[iamriajul]

Summary

• install the pinned pnpm version before setup-node cache restore
• enable setup-node pnpm store caching keyed by vibe-kanban/pnpm-lock.yaml
• cache Cargo registry/git data and the vibe-kanban target workspace for repeated release builds

Notes

• This should reduce repeated dependency install and Rust compile time after the first cache-warming run.
• It does not cache apt or AWS CLI installation; that step is much shorter after the OIDC workflow update, and avoiding system-level apt cache keeps this PR lower risk.

Verification

• YAML parse for .github/workflows/publish-npm.yml
• git diff --check