nats declares its own server settings, and where the mesh's users go

The split the controller now makes, from this side. The module's own
configuration — ports, TLS, JetStream — is a declared file resource, because those
are properties of this container and change when its image does. `bus-users` names
where the mesh writes every account and permission, in the same directory, and the
module's configuration includes it.

**Both files in one directory because they have to be.** An absolute include path
is resolved relative to the including file's directory: nats-server given
`include /etc/nats/accounts.conf` from /etc/nats-server/nats.conf looks for
/etc/nats-server/etc/nats/accounts.conf and refuses to start. Verified against the
server, and recorded in the configuration itself where somebody moving a file will
read it.

**`verify: true` is gone, and it was refusing every connection in the mesh.** It
makes the server demand a client certificate; a host pins this server's exact
certificate and authenticates with the password the mesh minted, and presents none.
Found by building this image and connecting to it as a host would.

The entrypoint now waits for both files and watches the mesh's half: the module's
own does not change without a new declaration, and that recreates the container
anyway. Verified end to end against this image — the mesh's user list rewritten,
the module noticing and reloading the server itself with no signal from outside,
and the connection the mesh already had still working afterwards.

modules/nats/module.json

@@ -13,6 +13,7 @@
       "scope": "mesh"
     }
   ],
+  "bus-users": "/var/lib/nats-module/conf/accounts.conf",
   "capabilities": [
     "container-runtime"
   ],
@@ -42,6 +43,13 @@
       "path": "/var/lib/nats-module/conf",
       "mode": "0700"
     },
+    {
+      "id": "server-conf",
+      "type": "file",
+      "path": "/var/lib/nats-module/conf/nats.conf",
+      "content": "# The nats module's own server settings. Declared by the module, because a port, a TLS path\n# and a store directory are properties of the container this module raises: they live in its\n# image and its mounts and change when it does.\n#\n# The mesh writes accounts.conf beside this one and nothing else. A controller that wrote the\n# whole file would have to be kept in step with a Dockerfile it never sees.\n\nport: 4222\nhttp: 127.0.0.1:8222\n\ntls {\n  cert_file: \"/tls/tls.crt\"\n  key_file: \"/tls/tls.key\"\n  ca_file: \"/tls/ca.crt\"\n}\n\n# **No `verify`, deliberately, and it was `verify: true` until a probe ran this image.** That\n# setting makes the server demand a *client* certificate, and nothing in the mesh presents one: a\n# host pins this server's exact certificate and authenticates with the password the mesh minted\n# (novox/hq ADR 0004, design 25 \u00a74), and so does a module's runtime. With it on, every connection\n# in the mesh is refused at the TLS handshake, before any password is looked at \u2014 and the error is\n# \"client didn't provide a certificate\", which reads as a client fault.\n#\n# TLS is still required: a tls block is what makes it required, and verify only decides whether\n# client certificates are checked. What is given up is a second factor the mesh has no machinery\n# to issue or rotate \u2014 a certificate per module per node \u2014 and what is kept is stronger than a\n# name check in both directions: an exact pin outward, a per-user password inward.\n\njetstream {\n  store_dir: \"/data\"\n}\n\n# Every user of the mesh, composed by the controller and rewritten whenever a module is\n# assigned, a node enrols or a person's access changes.\n#\n# **Relative, and in this same directory, because it has to be.** An absolute include path is\n# resolved relative to the including file's directory, not from the root: nats-server given\n# `include /etc/nats/accounts.conf` from /etc/nats-server/nats.conf looks for\n# /etc/nats-server/etc/nats/accounts.conf and refuses to start. Verified against the server.\ninclude accounts.conf\n",
+      "mode": "0644"
+    },
     {
       "id": "server",
       "type": "container",