[Air000000]

Summary

Adds a Chinese/English README switch modeled after the bilingual navigation pattern used by bojieli/ai-agent-book.

Changes

• makes the root README.md the default Chinese showcase page;
• adds docs/en/README.md as the English version;
• adds reciprocal language switch links at the top of both pages;
• keeps the same product-first / engineering-evidence structure in both languages;
• keeps v0.1.0 download, privacy, engineering, architecture, validation, and Yin Yue sections aligned;
• preserves the hidden media insertion slot without referencing missing GIF/PNG files.

Scope

Documentation only. No product/runtime code is changed.