Sync AI Chat supported models with upstream Docs

[Copilot]

The upstream Docs changed for aichat, and the local AI Chat integration guide had drifted from the current OpenAPI spec. This PR aligns the documented /aichat/conversations supported model list with the latest upstream source.

• AI Chat docs sync

  • Updated aichat/docs/aichat_conversations_api_integration_guide.md
  • Added the missing glm-5.2 model to the documented model enum for /aichat/conversations

• Scope

  • No endpoint, auth, request/response, or example changes
  • No changes outside the aichat/ docs

- ..., `grok-3`, `glm-5.1`, `glm-4.7`, ...
+ ..., `grok-3`, `glm-5.2`, `glm-5.1`, `glm-4.7`, ...