docs: add bilingual streamlined README and support code

[superche]

Summary

• replace the 581-line root README with a focused 193-line English landing page
• add a matching 193-line Simplified Chinese README at README.zh-CN.md, with language switching links in both files
• organize both versions around installation, first use, integration choices, architecture, local development, and documentation navigation
• route implementation details to the existing architecture, integration, package, OpenAPI, and release-engineering sources
• add a support section with the provided Buy Me a Coffee QR code

Impact

The repository now has concise English and Chinese entry points that are faster to scan and less likely to become stale. Runtime behavior and public contracts are unchanged.

Validation

• git diff --check
• verified both README files contain matching sections and 193 lines
• verified every new local README link resolves to an existing file
• verified assets/buy-me-a-coffee.jpg is a valid 1152×1152 JPEG

Full code tests were not run because this PR changes documentation and a static image only.