feat(streams): add WebSocket v1 client protocol contract (#3763)

## Summary & Motivation

Defines the `workflow-stream-ws/v1` frame schemas and encoder in `@workflow/world-vercel`, versioned independently of the REST API and workflow spec so a framing or acknowledgement change needs a new endpoint rather than a spec bump. Nothing calls it yet.

## Test Plan

Protocol tests added, including a byte-for-byte check against workflow-server's canonical frame fixture.