Surface unified AI Gateway models from the Workers AI model search experience

### Existing documentation URL(s)

- https://developers.cloudflare.com/workers-ai/models/
- https://developers.cloudflare.com/ai/models/
- https://developers.cloudflare.com/ai/models/deepseek/deepseek-v4-pro/

### What changes are you suggesting?

The Workers AI Models page includes a link to the unified AI model catalog, but model search on this page only returns Workers AI / Cloudflare-hosted models.

That distinction is technically correct, but it can be confusing for users who are trying to answer a broader question like “which models can I use through Cloudflare’s AI APIs?” rather than “which models are specifically hosted by Workers AI?”

Example: `deepseek/deepseek-v4-pro` has a public model page under the unified AI catalog:

https://developers.cloudflare.com/ai/models/deepseek/deepseek-v4-pro/

But searching or browsing from:

https://developers.cloudflare.com/workers-ai/models/

does not surface it, because it is an AI Gateway / unified AI model rather than a Workers AI model.

Could the Workers AI model search experience also surface unified AI Gateway models, with a clear visual affordance that they are different from Workers AI models? For example:

- show proxied / unified AI Gateway models in search results when they match the query
- label them as “AI Gateway”, “External provider”, or “Unified AI model”
- link those results to `/ai/models/...`
- preserve the existing “Cloudflare-hosted” / Workers AI labeling for native Workers AI models

This would help users discover available models without needing to know upfront whether a model belongs to Workers AI or AI Gateway.

### Additional information

The existing “Looking for more models, including external providers?” link is useful, but it is easy to miss when using the Workers AI model page as the main discovery surface.