amqp-ping declares a broker secret it never mounts

Its runtime is a tool host: it connects to the mesh's broker before it does
anything else. The module declares own-secrets.broker, and then its container
neither mounts that file nor names it, so the runtime started and said there was
no broker to reach, forever, in a restart loop.

lavinmq's runtime container does both, and is the shape this follows.

Claude-Session: https://claude.ai/code/session_01D6qtiYU3P9jk3pnAXyAFyx

modules/amqp-ping/module.json

@@ -48,6 +48,12 @@
       "type": "container",
       "name": "amqp-ping",
       "network": "amqp-ping",
+      "volumes": [
+        "/var/lib/mesh/amqp-ping/broker:/run/secrets/broker:ro"
+      ],
+      "env": {
+        "MESH_BROKER_FILE": "/run/secrets/broker"
+      },
       "env-file": [
         "/var/lib/amqp-ping/amqp.env"
       ],