feat: Add zh-CN translation & TOC script

[melxy1997]

This PR introduces two main features:

1. Simplified Chinese (zh-CN) Translation

• Added a full Simplified Chinese translation for the entire course.
• The initial translation was generated by an LLM and has been fully reviewed and polished by a human.
• During the manual review, we focused on:
  • Ensuring consistent terminology.
  • Retaining key English terms where appropriate to maintain context.
  • Avoiding literal (word-for-word) translations in favor of natural, idiomatic phrasing.

2. Automated Table of Contents (TOC) Script

• Added a new script scripts/update_toc.py to automate the process of updating the table of contents. This will help maintain consistency as new content is added.