This PR switches the OpenRouter integration from fetching all models to fetching only the models specified in the user's account preferences. This will help improve the experience **The Problem** The previous implementation used the `/models` endpoint, which returned an exhaustive list of all models supported by OpenRouter. This resulted in a long and cluttered model selection dropdown in Zed, making it difficult for users to find the models they actually use. **The Solution** We now use the `/models/user` endpoint. This API call returns a curated list based on the models and providers the user has selected in their [OpenRouter dashboard](https://openrouter.ai/models). Ref: [OpenRouter API Docs for User-Filtered Models](https://openrouter.ai/docs/api-reference/list-models-filtered-by-user-provider-preferences) Release Notes: - language_models: Support OpenRouter user preferences for available models