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/Dockerfile

@@ -13,7 +13,7 @@ ARG RUNTIME_BASE
 FROM ${BUILD_BASE} AS build
 WORKDIR /app/modules/nodered
 COPY . .
-RUN node /app/node_modules/typescript/bin/tsc client.ts tools/index.ts \
+RUN node /app/node_modules/typescript/bin/tsc client.ts tools/index.ts mqtt/probe.ts mqtt/connection.ts mqtt/index.ts \
       --module NodeNext --moduleResolution NodeNext --target ES2022 --outDir dist
 
 FROM ${RUNTIME_BASE}
@@ -22,3 +22,6 @@ COPY --from=build /app/modules/nodered/dist /app/modules/nodered/dist
 # provider's provisioner runs its reconcile loop in the same process, with the broker connected —
 # the convention novox/hq issues 060/061 settled.
 ENV MESH_TOOL_MODULES=/app/modules/nodered/dist/tools/index.js
+# NOT dist/mqtt/index.js: that is a step the host runs to completion, named by the `mqtt`
+# container's args as `mesh-tools run …` (novox/hq ADR 0052). Listed here it would run inside the
+# serving sidecar too, and exit it.