Clarify Agent docs

[MuncleUscles]

• Improve NavigationBrain description
• Clarify Execution Brains is an abstract concept not a concrete class
• Add Action-Brain Map section

[netlify[bot]]

✅ Deploy Preview for genworlds ready!

Name	Link
🔨 Latest commit	ab5f27fcd0325d5b350b820899da597e53b75535
🔍 Latest deploy log	https://app.netlify.com/sites/genworlds/deploys/64c96177d047120008cba5bd
😎 Deploy Preview	https://deploy-preview-27--genworlds.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.