Fix pnpm version mismatch in GitHub Actions workflow

Remove explicit pnpm version from workflow to use packageManager field in package.json, preventing ERR_PNPM_BAD_PM_VERSION errors.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: riglar

.github/workflows/build-source.yaml

@@ -30,8 +30,6 @@ jobs:
 
       - name: Setup pnpm
         uses: pnpm/action-setup@v4
-        with:
-          version: 9
 
       - name: Install Dependencies
         run: pnpm install