feat(core): mark reasoning summary as markdown callout (#12176)

Close [AI-75](https://linear.app/affine-design/issue/AI-75)

![截屏2025-05-07 17.40.32.png](https://graphite-user-uploaded-assets-prod.s3.amazonaws.com/sJGviKxfE3Ap685cl5bj/e5e7cf4c-0f80-41de-bb22-79a25fdfef48.png)

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

- **New Features**
  - Improved formatting for AI-generated reasoning and web search results, displaying them as callout blocks for enhanced readability.
  - Expanded support for rendering callout blocks in the text renderer.

- **Style**
  - Adjusted layout to ensure callout blocks retain appropriate spacing and appearance.

- **Refactor**
  - Simplified and unified the integration of web search tools for AI providers.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/server/src/plugins/copilot/tools/web-search.ts

@@ -4,7 +4,7 @@ import { z } from 'zod';
 
 import { Config } from '../../../base';
 
-export const createExaTool = (config: Config) => {
+export const createExaSearchTool = (config: Config) => {
   return tool({
     description: 'Search the web for information',
     parameters: z.object({