docs: translate module docs to Chinese (#1691)

[nuthalapativarun]

Description

Translate module documentation from English to Chinese.

Files added:

• docs/cn/open_source/modules/model_backend.md
• docs/cn/open_source/modules/api_deployment.md
• docs/cn/open_source/modules/mos/memos_mcp.md
• docs/cn/open_source/modules/mos/memos_neo.md

Class names, API names, code blocks, and command examples remain in English. Only explanatory prose is translated.

Related Issue (Required): Fixes #1691

Type of change

• 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?

• 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

[hijzy]

The CI Ruff checks are failing and need to be fixed before this can be merged:

• tests/api/test_mcp_serve.py has 2 unused imports. ruff check fixed them automatically, which means the committed file is not clean.
• ruff format --check reports that tests/api/test_mcp_serve.py needs formatting.

Please run locally:

poetry run ruff check --fix tests/api/test_mcp_serve.py
poetry run ruff format tests/api/test_mcp_serve.py