Add ScoutEngine.deliver_pending(user_id, ws) that queries status='queued'
rows, fetches metadata via the registered connector, sends scout_proposal
WS frames, and flips status to 'delivered'. Add ack_proposal(proposal_id)
that flips 'delivered' -> 'acked' (idempotent). Wire both into device_ws.py:
deliver_pending fires as a background task after device_hello + register;
scout_proposal_ack frames dispatch to ack_proposal in the message loop.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
