fix: use native fetch instead of node-fetch dependency

- Removed unnecessary node-fetch import from bin/brainy.js
- Removed node-fetch import from brainy-mcp-server.js
- Native fetch available since Node 18, brainy requires Node 24.4.0+
- Reduces dependencies by 6 packages
- Avoids indirect deprecation warning from boolean package
- No impact on browser compatibility (CLI is Node-only, core library unaffected)

Architecture notes:
- Brain Cloud integration remains as augmentation option
- Users can choose: local (free), Brain Cloud (9/mo), or self-host
- Clean separation maintained: brainy (MIT) vs Brain Cloud (proprietary)
- TODO: Consider extracting Brain Cloud specific URLs to config

brainy-mcp-server.js

@@ -12,7 +12,7 @@ import {
   ListToolsRequestSchema,
   Tool,
 } from '@modelcontextprotocol/sdk/types.js';
-import fetch from 'node-fetch';
+// Use native fetch (available in Node.js 18+)
 
 // Configuration from environment
 const CUSTOMER_ID = process.env.CUSTOMER_ID || 'demo-test-auto';