mosquitto: a consumer's grant is the topics it asks for, and its binding says the port

mqtt-topic served nothing: with two listens the mesh could not say which port a consumer dials, so a
consumer had to type 1883 into its config. It now serves the MQTT listener's port (the machine's,
once assigned) and the scheme, so `${bound:mqtt-topic:port}` fills.

The provisioner confined every consumer to `<as>/#`, which leaves nothing for the consumers the
broker exists for: Home Assistant discovers under homeassistant/# and tasmota/discovery/#, and
Node-RED's flows follow the devices' own topics. A consumer now contributes `topics` (MQTT topic
filters) to its mqtt-topic requirement and is granted exactly those; with none, its own subtree as
before. Settings merge into contributions, so an operator narrows a grant per assignment. The role
is brought to exactly the wanted ACLs (stale ones removed), `holds` checks the ACLs too, and an
invalid list is refused, never quietly narrowed. Only the role named for the consumer is touched:
a client carried from the predecessor's password file keeps its own.

modules/mosquitto/module.json

@@ -20,7 +20,10 @@
     "mosquitto.topic.deprovisioned"
   ],
   "serves": {
-    "mqtt-topic": {}
+    "mqtt-topic": {
+      "scheme": "mqtt",
+      "port": 1883
+    }
   },
   "receives": {
     "mqtt-topic": "${dir:grants}/mesh.json"