docs: complete IaC Code Skill documentation

[guima-why]

Summary

• add an official Skills overview comparing iac-code, alibabacloud-iac-code, and alibabacloud-ros-agent
• complete the installation and usage guide plus the host integration reference
• connect the new overview from the documentation home, A2A overview, README files, related links, and sidebar
• provide natural translations for all seven supported documentation languages
• add regression coverage for Skill documentation content and sidebar registration
• leave Desktop documentation unchanged

Testing

• uv run pytest -q tests/test_website_skill_docs.py
• uv run ruff check tests/test_website_skill_docs.py
• npm test (website)
• npm run build (website, all seven locales)