Fix dashboard example createGoogle()

The dashboard says use `createGoogle()`, but after a lot of search I found, it's `createGoogleGenerativeAI()`

https://github.com/cloudflare/ai/blob/3bea0a571e3b6ee2140e25d3ac76535346a01212/packages/ai-gateway-provider/src/providers/index.ts#L10

<img width="770" height="539" alt="Image" src="https://github.com/user-attachments/assets/7433e5d7-059e-4030-afd2-55b7d18e7702" />