Add Simplified Chinese (zh-CN) translation for all documentation

[dowithless]

What problem are you trying to solve?

This PR introduces the Simplified Chinese (zh-CN) translation for all Markdown (.md) files in the repository. The goal is to make the project more accessible to the Chinese-speaking community.

What does this PR change?

• Translated all existing documentation from English to Simplified Chinese.
• Maintained the original Markdown structure and formatting.
• All translated files are organized within a dedicated zh-CN/ folder.

Is this change appropriate for the core library?

What alternatives did you consider?

Does this PR contain multiple unrelated changes?

Existing PRs

• I have reviewed all open AND closed PRs for duplicates or prior art
• Related PRs:
• docs: add chinese README.zh.md #713

Environment tested

Harness (e.g. Claude Code, Cursor)	Harness version	Model	Model version/ID

Evaluation

• What was the initial prompt you (or your human partner) used to start
  the session that led to this change?
• How many eval sessions did you run AFTER making the change?
• How did outcomes change compared to before the change?

Rigor

• If this is a skills change: I used superpowers:writing-skills and
  completed adversarial pressure testing (paste results below)
• This change was tested adversarially, not just on the happy path
• I did not modify carefully-tuned content (Red Flags table,
  rationalizations, "human partner" language) without extensive evals
  showing the change is an improvement

Human review

• A human has reviewed the COMPLETE proposed diff before submission