Support [AI-59](https://linear.app/affine-design/issue/AI-59)
Deprecated use of the perplexity model. Makes chat and search use the same prompt content.
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- **New Features**
- Added support for two new AI models: Claude Opus 4 and Claude Sonnet 4, enabling enhanced text and image input capabilities.
- Introduced a new chat prompt with detailed instructions for specialized AI interactions within AFFiNE.
- **Refactor**
- Improved prompt management for AI chat and search features by centralizing shared settings for better consistency.
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