fix AI-398
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## Summary by CodeRabbit
* **New Features**
* Added support for specifying fallback models for multiple AI
providers, enhancing reliability when primary models are unavailable.
* Providers can now fetch and update their list of available models
dynamically from external APIs.
* Configuration options expanded to allow custom base URLs for certain
providers.
* **Bug Fixes**
* Improved model selection logic to use fallback models if the requested
model is not available online.
* **Chores**
* Updated backend dependencies to include authentication support for
Google services.
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