After the #872 MQTT wiring, the JSON->VitalsSnapshot bridge hard-coded a
single node_id (the MQTT client id) and the publisher used one
OwnedDiscoveryBuilder, so every physical node collapsed into a single
Home-Assistant device (identifiers:["wifi_densepose_wifi-densepose-1"]),
contradicting the one-device-per-node docs.
- Bridge (main.rs): emit one VitalsSnapshot per node in the sensing
update's nodes[] (each carries its own node_id + RSSI; shared aggregate
presence/vitals), falling back to a single aggregate snapshot when
there is no per-node data (wifi/simulate sources).
- Publisher (publisher.rs): add OwnedDiscoveryBuilder::for_node(), and
publish discovery + availability lazily on first sight of each node_id,
routing state to per-node topics. Heartbeat/refresh/offline-LWT iterate
all known nodes. Result: N distinct HA devices, one per node.
3 new unit tests (distinct nodes -> distinct wifi_densepose_<node>
identifiers); full MQTT suite 71 passed, example builds.
9ddcf0c9fc