LIVE_CAPABILITY

A fabric with no live OS path observer, so us.tractat.kuilt.core.Seam.capability is a static us.tractat.kuilt.core.FabricAvailability.Unknown floor rather than a reactive value. A fabric gap, not a harness gap: the platform observer simply has not been wired yet. Track B (#1542 multipeer, #1543 nearby, #1544 webrtc, #1545 composite, #1546 mux, #1725 websocket) closes these one lane at a time.