nodered: its MQTT broker comes from the mesh

Node-RED's one broker node pointed at zurag.be:1884, where nothing listens. nodered now requires
mqtt-topic (asking for every topic: flows follow the devices' own) and a run-once `mqtt` step —
declared last, restarted when the binding, credential or settings change — points the mesh's broker
nodes at the bound broker through Node-RED's admin API with the module's api-token: the node the
step makes itself when none is named, or the ones an assignment names in `mqtt.brokers`. Only host,
port, TLS and the login change; the broker is asked first whether it takes the login; the deploy is
against the revision read ("nodes", so only that node restarts) and a digest makes a rerun a no-op.
A broker node nobody named is never touched. settings.js keeps `mqtt` and `topics` out of Node-RED.

modules/nodered/tsconfig.json

@@ -8,5 +8,11 @@
     "skipLibCheck": true,
     "noEmit": true
   },
-  "include": ["client.ts", "tools/index.ts"]
+  "include": [
+    "client.ts",
+    "tools/index.ts",
+    "mqtt/probe.ts",
+    "mqtt/connection.ts",
+    "mqtt/index.ts"
+  ]
 }