Add Agno integration docs and redirect Phidata entry

[prrao87]

Summary

• replace the Phidata integration with a dedicated Agno page that walks through LanceDB-backed knowledge ingestion, prompting, and chat iteraction
• update docs navigation and redirects so the new Agno page sits under the AI integrations group and the old Phidata path forwards to it
• refresh snippet catalog with the Agno onboarding fragments that power the new tutorial