AI Transport v0.6.0: mid-run steering

What this post added

Introduces the 'steering' capability to AI Transport, allowing clients to redirect an agent mid-run. Implements the `steer(...)` method on active Runs for sending follow-up prompts and the `onSteer(...)` hook in `session.createRun` to abort in-flight model calls. The agent's loop is modified to check `run.hasInput()` for steering messages and to use `AbortSignal.any` with a new `stepAbort` controller to interrupt model calls. The client-side `consumed` flag is updated to reflect whether the steering message was acted upon.