feat(core): add ai model switch ui (#12266)

Close [AI-86](https://linear.app/affine-design/issue/AI-86)

![截屏2025-05-14 11.32.41.png](https://graphite-user-uploaded-assets-prod.s3.amazonaws.com/sJGviKxfE3Ap685cl5bj/b92d5c32-fa5a-4afd-93e6-3699347575be.png)

<!-- This is an auto-generated comment: release notes by coderabbit.ai -->

## Summary by CodeRabbit

- **New Features**
  - Introduced AI model switching in chat, allowing users to select from multiple AI models during conversations.
  - Added a floating menu for easy AI model selection within the chat interface.
  - Enabled visibility of the AI model switcher through a new experimental feature flag, configurable in workspace settings (canary builds only).

- **Enhancements**
  - Improved session management in the chat panel for smoother model switching and state handling.
  - Updated localization to support the new AI model switch feature in settings.

- **Bug Fixes**
  - None.

- **Chores**
  - Registered new components and services to support AI model switching functionality.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/server/src/plugins/copilot/prompt/prompts.ts

@@ -1066,6 +1066,7 @@ const chat: Prompt[] = [
     name: 'Chat With AFFiNE AI',
     model: 'gpt-4.1',
     optionalModels: [
+      'gpt-4.1',
       'o3',
       'o4-mini',
       'claude-3-7-sonnet-20250219',