feat: Add Browserbase search and fetch support to the n8n node

[Kylejeong2]

Summary

• rename the node from Browserbase Agent to Browserbase
• add Browserbase Search and Fetch as first-class resource options alongside Agent
• update the README, node metadata, package version, and official Browserbase icon from the media kit

Implementation details

• Agent continues to use the Stagehand session endpoints
• Search now calls POST /v1/search
• Fetch now calls POST /v1/fetch
• credentials now validate against the Browserbase Fetch API
• package version is bumped from 1.2.4 to 1.3.0

Verification

• npm run lint
• npm run build