wren node: targets from the wiring, on wren 2

Every output is a target and every input besides prompt a reading. A
targets setting gives descriptions, values, ranges and per-target
guards, model takes a trained pack's artifact digest, min_confidence
defaults to the model's threshold. A command is applied whole or not at
all, and targets the model was not trained on read degraded. The home
path (area/kind ports, groups, brightness, temperature answers) is gone.

docs/code/agents.md

@@ -77,6 +77,6 @@ which is where a `stt` node writes what a device heard, so typed and spoken
 commands are one conversation: the words heard so far, the command, each
 reply, and the reported actions with their target message, value and whether
 each was applied. A node whose prompt is another's `unhandled` answers in that
-node's conversation. Wren's `apply` and `min_confidence` settings decide
-whether it writes to devices. Control conversations stay in the browser and
-clear on reload.
+node's conversation. Wren's `apply`, `min_confidence` and `targets` settings
+decide whether it writes to its targets. Control conversations stay in the
+browser and clear on reload.