feat(example): add Exa-powered web search via ChatService

[tgonzalezc5]

Summary

• Adds ExaChatService, a drop-in ChatService implementation powered by Exa (AI-native search engine) so Eko's built-in WebSearchTool returns real, structured search results instead of empty arrays
• Uses the exa-js SDK v2 with search() + highlights for token-efficient agent pipelines
• Includes the x-exa-integration: eko header for integration-level usage tracking (see also HKUDS/CLI-Anything#205 for the same pattern in another open-source integration)
• Wires into the Node.js example with a single env var (EXA_API_KEY)

How it works

Eko's WebSearchTool delegates to global.chatService.websearch(), which currently returns [] in the example SimpleChatService. This PR provides a real implementation:

import { ExaChatService } from './exa-chat-service';
global.chatService = new ExaChatService(); // reads EXA_API_KEY from env

Exa results are mapped to Eko's WebSearchResult type (title, url, snippet, content), and highlights are used as the snippet for optimal token efficiency.

Files changed

File	Change
example/nodejs/src/exa-chat-service.ts	New ExaChatService implementation
example/nodejs/src/index.ts	Wire up Exa when EXA_API_KEY is set
example/nodejs/package.json	Add exa-js dependency

Test plan

• Set EXA_API_KEY in .env and run the Node.js example
• Verify WebSearchTool returns Exa results (title, url, snippet, content)
• Verify example still works without EXA_API_KEY (graceful no-op)

Get an API key

Free keys available at dashboard.exa.ai/api-keys

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Disclosure: I work at Exa. Happy to iterate on feedback.