The forge's sidecar dials the port the machine put the forge on (hq issue 088)

MESH_GITEA_URL named 3000 outright. The forge's container publishes 3000 without
fixing the machine side, so the mesh assigns it — and on a node given that port
as a setting it is the operator's number. The mapping that lets the forge go on
binding 3000 does nothing for a caller dialling the machine's loopback, so the
sidecar dialled a port nothing was listening on wherever the two differed.

${port:3000} is the mesh's answer to exactly that question, and it now resolves
in a container's environment as it always has in a file. The forge declares it
listens on 3000, so it may ask.

Still names 3000: the route contribution (hq issue 089) and the `listens` and
`ports` entries, which are the software's own number and belong there.

modules/gitea/module.json

@@ -165,7 +165,7 @@
       ],
       "env": {
         "MESH_BROKER_FILE": "/run/secrets/broker",
-        "MESH_GITEA_URL": "http://127.0.0.1:3000",
+        "MESH_GITEA_URL": "http://127.0.0.1:${port:3000}",
         "MESH_GITEA_CONFIG_FILE": "/run/config/config.json",
         "MESH_GITEA_ADMIN_USER": "mesh-admin",
         "MESH_GITEA_ADMIN_PASSWORD_FILE": "/run/secrets/admin",