docs: add Simplified Chinese translation (README.zh.md)

[JasonYeYuhe]

This PR adds a comprehensive Simplified Chinese translation (README.zh.md) to the repository and introduces a highly visible language switcher just below the hero banners in the main README.md.

Motivation:
As the claw harness and the UltraWorkers toolchain continue to gain significant attention globally, providing native localization dramatically lowers the barrier to entry for the massive Chinese-speaking developer community. This ensures more users can easily understand the project philosophy (agent-managed exhibit vs. hand-operated product) and get started with the correct harnesses (LazyCodex / Gajae-Code).

Changes included in this PR:

1. Added README.zh.md: A full, high-quality, technically accurate translation of the main README.md.
2. Strict Parity: The translated document perfectly matches the structural parity of the English original (including all warnings, code blocks, and markdown structure).
3. Language Switcher: Inserted a clean English · 中文 switcher below the primary graphical banners in README.md.
4. Maintenance Tracker: Appended a maintainer tag to ensure future translation syncs can be routed appropriately.

Testing Conducted:

• Validated all markdown links (especially relative links to ./USAGE.md, ./rust/README.md, etc.) to ensure they point to the correct files.
• Confirmed that the markdown syntax renders perfectly on GitHub's UI.