星火传灯，首页留辉 · Add Star CTA, CONTRIBUTING.md, and CODE_OF_CONDUCT.md

[eric8810]

Summary

This PR adds community-building essentials to the repository.

Changes

• Star CTA in both English and Chinese READMEs — a friendly nudge after the "What you get" section
• CONTRIBUTING.md — build steps, test commands, bug reporting, feature proposals, PR process, and commit conventions
• CODE_OF_CONDUCT.md — Contributor Covenant v2.0
• Updated "Community and license" section in both READMEs to link to the new files

Why

The repo is one week old and already at 326 stars, but it was missing:

• A call-to-action for stars (proven to increase conversion from visitors to stargazers)
• Clear contribution guidelines to lower the barrier for first-time contributors
• A code of conduct to signal a welcoming, professional community

These are files that most successful open-source projects have in place from the start.