Translate evaluation docs to Chinese

[CaralHsi]

The evaluation documentation currently exists only in English. This issue is to add Chinese translations for the evaluation docs.

Files to translate

Translate:

• docs/en/open_source/evaluation/overview.md
• docs/en/open_source/evaluation/openai_memory_locomo_eval_guide.md

Place the translated files under:

• docs/cn/open_source/evaluation/overview.md
• docs/cn/open_source/evaluation/openai_memory_locomo_eval_guide.md

Requirements

• Preserve command examples and script paths exactly.
• Keep dataset names such as LoCoMo, LongMemEval, PrefEval, and PersonaMem unchanged.
• Use clear Chinese explanations for setup, configuration, and evaluation workflow.
• Ensure relative links still work from the new Chinese docs location.

Acceptance Criteria

• Both Chinese evaluation pages are added.
• Markdown formatting is valid.
• Code blocks and commands remain unchanged.
• Links between the overview page and the OpenAI Memory guide work correctly.