Azure Web PubSub

### Feature Summary

Support for Azure Web Pub Sub

### Feature Description

It would be great if we had native support for https://learn.microsoft.com/en-us/azure/azure-web-pubsub/.
We're looking at using this for Agency, on the backend, but our CLI that wants to stream and receive events is 100% Rust :)

### Use Case

Agency CLI Streaming agent sessions across devices

### Alternatives

Define our own messages in Rust, use schemars to generate Json Schema, and generate C# code to mirror these for use in the pub sub service.

### Additional Context

_No response_

Start with the Azure Web PubSub documentation linked in the issue and determine the SDK surface required for the Agency CLI's streaming and event-receiving use case. No files, tests, or entry points are named, so identify the relevant existing Rust SDK service pattern before implementation. Done means native Azure Web PubSub support for the stated use case, with appropriate validation and tests.

Written by the indexing model from the issue text.