docs(sso): add Keycloak tutorial and split sso.md files

[dezhishen]

Description / 描述

Motivation and Context / 背景

Closes #118

Relates to #XXXX

Checklist / 检查清单

• I have read the CONTRIBUTING document.
  我已阅读 CONTRIBUTING 文档。
• I have formatted my code or documentation with prettier or other appropriate formatter.
  我已使用 prettier 或其他适当的格式化工具格式化提交的代码或文档。
• I have updated all supported languages (including Chinese and English) for documentation. (If it's needed)
  我已为所有支持语言（包括中文和英文）更新文档内容。 (若适用)
• I have verified that the written documentation or code is properly formatted, with no syntax errors, spelling mistakes.
  我已确认编写的文档或代码格式正确, 无语法错误, 拼写错误。
• I have updated the repository accordingly (If it's needed).
  我已相应更新了相关仓库（若适用）。
  • OpenList #XXXX
  • OpenList-Frontend #XXXX

[Copilot]

Pull request overview

This pull request adds a Keycloak SSO tutorial and refactors the SSO documentation by splitting the monolithic sso.md file into separate, more maintainable files for each SSO provider.

Changes:

• Added comprehensive Keycloak integration tutorial (07-keycloak.md) with step-by-step instructions in both English and Chinese
• Split existing SSO documentation into separate files (01-GitHub.md through 06-Authentik.md)
• Updated main sso.md to use markdown includes for the split files
• Added three new screenshot images for the Keycloak tutorial

Reviewed changes

Copilot reviewed 8 out of 11 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
pages/guide/advanced/sso.md	Refactored to use includes for SSO provider sections, maintaining the same content structure
pages/guide/advanced/sso/01-GitHub.md	Extracted GitHub SSO tutorial from main file
pages/guide/advanced/sso/02-Dingtalk.md	Extracted Dingtalk SSO tutorial from main file
pages/guide/advanced/sso/03-Microsoft.md	Extracted Microsoft SSO tutorial from main file
pages/guide/advanced/sso/04-Google.md	Extracted Google SSO tutorial from main file
pages/guide/advanced/sso/05-Casdoor.md	Extracted Casdoor SSO tutorial from main file
pages/guide/advanced/sso/06-Authentik.md	Extracted Authentik SSO tutorial from main file
pages/guide/advanced/sso/07-keycloak.md	New comprehensive Keycloak SSO integration guide with bilingual instructions
public/img/advanced/sso/keycloak-01.png	Screenshot for Keycloak general settings
public/img/advanced/sso/keycloak-02.png	Screenshot for Keycloak capability configuration
public/img/advanced/sso/keycloak-03.png	Screenshot for Keycloak login settings

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