Docs/video speech update

[paullizer]

User Interface Enhancements

• AI Voice Conversations Setup Guide
  • Added an in-app Setup Guide modal to the AI Voice Conversations admin card so admins can configure Azure Speech without leaving Admin Settings.
  • The guide includes a live snapshot of the current Speech configuration, explains key versus managed-identity authentication, and now walks admins through enabling the required custom domain in Azure portal before verifying the endpoint on Keys and Endpoint.
  • (Ref: admin_settings.html, _speech_service_info.html, azure_speech_managed_identity_manul_setup.md, test_admin_multimedia_guidance.py)