This commit introduces a new `PageAssistSelect` component to the header, which replaces the previous `Select` component for selecting the active chat model. The new component provides improved functionality, including:
- Ability to display provider icons alongside the model name
- Truncation of long model names to ensure they fit within the available space
- Improved loading state handling
- Ability to refresh the model list on demand
These changes enhance the user experience and make it easier for users to quickly select the desired chat model.
