S23 Translation and Internationalization

S23 expands the current zh-Hans documentation site into a maintainable bilingual site.

Current status

The site currently uses zh-Hans as the primary language, and existing project Markdown is connected through symlinks.

Follow-up goals

• Create a parallel en/ directory.
• Translate README, docs/, ai-skills/, and core specs.
• Add MkDocs i18n configuration.
• Keep terminology, version numbers, installation commands, and backend policy consistent.

This task is suitable for a low-cost translation model. The main engineering work should retain only structure and acceptance standards.