[Feature]: 支持Gemini接入Google Cloud Vertex AI endpoint

### Problem or Motivation

目前的Gemini使用了 Gemini Developer 的 API，这个是个人版，限制非常多，希望接入企业版的 Vertex AI

这里是Google官方给出的建议：https://ai.google.dev/gemini-api/docs/migrate-to-cloud?hl=zh-cn

### Proposed Solution

希望能接入Google Cloud提供的Vertex AI中的Gemin和Claude模型，这个方式调用Gemini稳定性更好。

### Alternatives Considered

_No response_

### Area

Classroom generation

### Additional Context

_No response_

Start by reading the linked Google migration guide and locating the current Gemini Developer API integration used for classroom generation. Determine the configuration, authentication, and model-selection entry points involved; the work is done when Vertex AI supports the requested Gemini and Claude model access with stable classroom generation.

Written by the indexing model from the issue text.