Update Duo Workflow architecture diagrams in documentation

Problem

The architecture diagrams for Duo Agent Platform in the handbook documentation are outdated and do not reflect the current implementation. Specifically:

• The diagrams still refer to "Duo Workflow" instead of the current architecture
• They don't show WebSocket connections
• They don't show the node executor
• Customers and prospects need accurate architecture diagrams to present to their Security departments for validation of implementation options (SaaS vs Self-Managed)

This is blocking customer conversations and deal negotiations, as prospects cannot properly evaluate security and architecture requirements without up-to-date documentation.

Desired Outcome

Update the architecture diagrams in the handbook to accurately reflect the current Duo Agent Platform architecture, including:

Reference: For GitLab Dedicated deployments

• Architecture diagram (in progress via gitlab-com/content-sites/handbook!16480 (merged))