chore(server): update exa search tool description (#14682)

Updated the Exa search tool description to better reflect what Exa does.

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

* **Chores**
* Clarified the web search tool description to state it uses Exa, a web
search API optimized for AI applications to improve labeling and user
understanding.
* No functional or behavioral changes to the tool; this update affects
only the displayed description users see.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

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Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Co-authored-by: ishan <ishan@exa.ai>

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

@@ -7,7 +7,7 @@ import { defineTool } from './tool';
 
 export const createExaSearchTool = (config: Config) => {
   return defineTool({
-    description: 'Search the web for information',
+    description: 'Search the web using Exa, one of the best web search APIs for AI',
     inputSchema: z.object({
       query: z.string().describe('The query to search the web for.'),
       mode: z