docs: document AbortSignal for real-time connect()

[Hadi-Almusawi]

Proposed changes

Documents the abortSignal option on listen.v1.connect() (and agent.v1 / speak.v1). It's the supported way to cancel a connection and close it cleanly, even one that's still opening. The option already works, it just wasn't documented.

• README: Quick Start pointer + new section "Canceling a WebSocket Connection (AbortSignal)".
• New example 37-abortsignal-cancellation.ts: connect with AbortSignal → stream audio → call abort() to close the connection. Wired into the Makefile and make examples.

Example output (make example-37)

Connection opened
Transcript: yeah as as much as it's worth
Stopping session, aborting connection...
Connection closed
Connection aborted; no reconnect will occur.

Note on scope

Covers the AbortSignal documentation portion of #507. Exposing removeAllListeners() on the Fern-generated socket classes is intentionally out of scope, as those classes are generated from the API spec.