ci: add docs:build step to test workflows

[SoonIter]

Summary

Add docs:build script to package.json and include docs build step in both Windows and macOS test workflows.

Changes

• Add docs:build script in package.json that runs pnpm -r --filter=./packages/**/* run docs:build
• Add "Build Docs" step in .github/workflows/test-Windows.yml
• Add "Build Docs" step in .github/workflows/test-macOS.yml

This ensures all workspace documentation can be built successfully during CI tests.