fix realtime websocket dependency contract

[lyonsno]

Context

The repo exposes a realtime transcription websocket endpoint and the frontend connects to it, but the published extras only install bare uvicorn. On a fresh install, websocket upgrades fail unless users manually add websockets or
uvicorn[standard].

What this changes

• adds websocket support to the server extra
• adds websocket support to the all extra
• adds optional-dependency tests to verify the advertised install contract covers realtime STT

Why this is useful

This makes the fresh-install path match the actual runtime behavior expected by the realtime UI and server.

[Blaizzy]

Closing as AI slop.

We use Fastapi for websockets.