Add Chinese (Simplified) translations for all documentation, organized
under a dedicated zh/ directory that mirrors the English folder structure.
Co-authored-by: tanqingkuang <tanqingkuang@users.noreply.github.com>
Translations originally contributed by @tanqingkuang in #45.
Restructured from *-CN.md suffix pattern into zh/ directory to prevent
the EPUB builder (scripts/build_epub.py collect_folder_files) from
picking up Chinese files via glob("*.md") inside module folders.
Luong NGUYEN