Fix #1692: Translate evaluation docs to Chinese

[Memtensor-AI]

Description

已完成 evaluation 文档的中文翻译：新增 docs/cn/open_source/evaluation/overview.md 与 openai_memory_locomo_eval_guide.md，保留了 LoCoMo / LongMemEval / PrefEval / PersonaMem 等数据集名、所有命令与脚本路径，以及 ../../../../evaluation/scripts/... 相对链接（已校验可解析到仓库根的 evaluation/scripts/）。Commit 已 push 到 autodev/MemOS-1692。

Related Issue (Required): Fixes #1692

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactor (does not change functionality, e.g. code style improvements, linting)
• Documentation update

How Has This Been Tested?

Not run; documentation-only change.

• Unit Test
• Test Script Or Test Steps (please provide)
• Pipeline Automated API Test (please provide)

Checklist

• I have performed a self-review of my own code | 我已自行检查了自己的代码
• I have commented my code in hard-to-understand areas | 我已在难以理解的地方对代码进行了注释
• I have added tests that prove my fix is effective or that my feature works | 我已添加测试以证明我的修复有效或功能正常
• I have created related documentation issue/PR in MemOS-Docs (if applicable) | 我已在 MemOS-Docs 中创建了相关的文档 issue/PR（如果适用）
• I have linked the issue to this PR (if applicable) | 我已将 issue 链接到此 PR（如果适用）
• I have mentioned the person who will review this PR | 我已提及将审查此 PR 的人

@CarltonXiang, @syzsunshine219 please review this PR.

Reviewer Checklist

• closes Translate evaluation docs to Chinese #1692
• Made sure Checks passed
• Tests have been provided