Seed the aircon write-path rig

Four controls and the unit's own answer beside them. Two catches, both on:
the flow is seeded stopped and the node's commands setting is off. The initial
values are read off the unit when the script runs, so starting the flow asks
for what it was already doing rather than commanding it to something else.

NOTEPAD.md

@@ -69,7 +69,10 @@ end against the house broker. The rig is the `house_control` flow and its
 dashboard, seeded by `make -C app seed-house`.
 
 - FEAT/NODE: Art-Net against the real fixtures is still untried. The house's own dmxnet sender re-emits universe 1 every 1000 ms, so fluksio and Node-RED overwrite each other; the test needs Node-RED's Art-Net sender stopped, and while it is stopped every channel fluksio does not set is dark.
-- FEAT/NODE: the WF-RAC write path stays gated. `setAirconStat` needs an operatorId registered with the unit first, which is itself a write, and the aircon is not on the safe-to-control list.
+- FEAT/NODE: the aircon has never been commanded for real. The encoder round-trips the unit's own live reading field for field and the dry run logs the right command, but nothing has been posted to it yet. `commands` is the switch.
+- CHORE/NODE: the operatorId worry was unfounded — the reference Node-RED `setstat` node for this unit is configured with an empty operatorId and deviceId, so a command needs no registration. The second unit may still differ.
+- PERF/NODE: a `wfrac` command is two round trips (read, then set) on the scheduler's thread, so at the default timeout a command can hold a cascade for several seconds. Fine for a person pressing a button; a flow commanding it on a schedule would want the work off that thread.
+- CHORE/NODE: `wfrac` writes carry the unit's whole state, so two flows commanding one unit will each undo whatever the other set between their read and their write. One writer per unit, the same rule Art-Net has for a universe.
 - FEAT/NODE: the second WF-RAC unit (the one Node-RED addresses with operatorId "0") closes the connection on an anonymous read. It likely wants an account registered; the first unit answers without one.
 - CHORE/NODE: `wfrac` reports `mode` as "unknown" while the unit is off, because the mode bits hold a value outside the known set. Faithful to the reference decoder, but "off" would read better.
 - PERF/NODE: `ArtNetOut.write` sends one frame per input port, so a node with two ports emits two frames per run. The last one carries both channels, so the end state is right; folding them into one send would halve the traffic.