nudge.py: surface repeated queue fallbacks to the host nw agent

queue_push() fails closed correctly (nothing queued, nothing acked, falls back to send-keys) but the only signal that this keeps happening is a stderr line in the user journal that nobody reads. The script's own header records an 11-day silent miss of exactly this shape. Proposal: count consecutive fallbacks/refusals per agent in the state file; on the Nth consecutive one (N=3) DM the host nw agent (nw-<host>-cc) once with the reason line, then stay quiet until it clears. Same one-shot pattern as MODE_STUCK_CANCEL_CYCLES.