fix: commit pnpm-lock.yaml and remove it from .gitignore

The lockfile must be tracked so CI can use --frozen-lockfile and
actions/setup-node cache can locate pnpm-lock.yaml.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: Zhang-JiahangH

.gitignore

@@ -3,4 +3,3 @@ dist
 coverage
 .vite
 .DS_Store
-pnpm-lock.yaml