Remove xyz link

* Fix README.md and README_KR.md which use the logo.
* Use a stripped, small (2.8 kiB), local SVG file.
* The file is from Wikimedia, license clean.

Enable GitHub Pages with the Cayman theme to publish
the documentation as a website.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Add Jekyll config for GitHub Pages

Use local SVG logo in README.

Update all internal links in README.md, README_CN.md, and README_KR.md
to use relative paths instead of absolute GitHub URLs. This allows the
links to work correctly on GitHub Pages, pointing to the generated HTML
pages rather than redirecting back to the repository.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Fix GitHub Pages links to use relative paths

Fix grammar issues throughout the repository's markdown files:
- Correct spelling errors (e.g., defination → definition, intepreter → interpreter)
- Fix capitalization at sentence starts
- Correct article usage and verb agreement
- Fix run-on sentences with proper punctuation
- Standardize technical terms (e.g., posix → POSIX, python → Python)
- Fix possessive vs contraction errors (it's → its)

Addresses issue #59

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Improve English grammar and readability across documentation