fix(docs): emit helper output as UTF-8

[dajiaohuang]

Summary

• configure the documentation helper's text stdout as UTF-8 when supported
• refresh the bundled helper copy used by packaged skill installs

This prevents successful Unicode documentation responses from failing during JSON output on Windows consoles with a legacy default encoding.

Fixes #49.

Validation

• python -m py_compile skills/vs-product-qa/references/volcengine-documentation/scripts/volcengine_docs.py
• fetched the documented Viking AI Search root on a default Windows console and parsed the emitted JSON successfully (2,361 Unicode content characters)
• npm run build
• npm run validate:skills
• git diff --check