Pi acks the prompt command only after slash-command expansion completes,
and extension commands can block on user dialogs indefinitely. Awaiting
the ack with a 15s timeout failed the turn mid-dialog and cancelled the
prompt the user was answering. Send prompt and steer fire-and-forget;
rejections come back as id-less response records and fail the turn from
the event pump. Found by exercising /commands against a real pi install.

Also carries concurrent review fixes staged in the shared worktree by
the review-babysitting agent: theme-aware Pi icons on web and mobile,
bounded RPC error summaries, and transport/request hardening in PiRpc.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>