Optimize repository experience and harden favicon fetching

[VeteranBoLuo]

What changed

• make English the default README and add a dedicated Simplified Chinese guide
• add a responsive interactive playground, Docker image, CI, tests, and community templates
• manually validate every redirect hop for SSRF protection and bound upstream response sizes
• fix prefixed health checks, stable 304 responses, unsafe URL handling, and misleading size behavior

Why

The repository explained the feature set well but lacked an immediate product demo and project maturity signals. The implementation also claimed per-redirect SSRF checks while relying on automatic redirects, and the deployed path prefix broke the documented health endpoint.

Impact

Visitors get a clearer English-first project page and a usable playground after deployment. Maintainers get dependency-free tests across supported Node.js versions plus a Docker build check. API users keep the same ?url= interface with stricter URL validation and safer redirect handling.

Validation

• npm run check — 11 tests passed
• manual HTTP smoke test — home 200, health 200, favicon 200, conditional request 304, private address 403
• YAML parse check for workflow and issue template
• live lookups verified for GitHub and Pexels
• Docker build deferred to CI because Docker is unavailable on the local machine