swarm: default every queue URL to the queue's name on every hive

A remote hive dialled nothing until an operator copied the queue's URL
into it, though the URL is the same string everywhere. statusPublish.natsUrl,
queue.agentNatsUrl and controller.queue.natsUrl now default to
tls://<swarm.nats.domain>:<port> unconditionally.

The statusPublish assertion treated a URL without a secret as a half
config. With the URL a default on every hive, only the secret claims
publishing: the assertion now refuses a secret without a URL or token
endpoint, and hive-c0re's status environment is gated on the secret too,
so a hive without one publishes nothing instead of reading a missing
credential.

nix/host-modules/hive-c0re/default.nix

@@ -133,12 +133,12 @@ in
     ./options.nix
     ./theme.nix
     # Hive-CA trust for this daemon's outbound TLS. Nothing it is given by
-    # default is https — the forge, matrix and queue URLs all resolve to
-    # plain http or loopback — so this changes nothing on an all-local
-    # hive. It matters for the split-host shape the options invite:
-    # `swarm.matrix.apiUrl`'s own example is `https://matrix.example.com`,
-    # and pointing it (or `deploy.hive-controller.statusPublish.natsUrl`)
-    # at another hive's
+    # default is https — the forge and matrix URLs resolve to plain http or
+    # loopback, and the queue's TLS is verified against
+    # `HIVE_C0RE_OIDC_CA_FILE` (../hive-tls.nix), not this bundle — so this
+    # changes nothing on an all-local hive. It matters for the split-host
+    # shape the options invite: `swarm.matrix.apiUrl`'s own example is
+    # `https://matrix.example.com`, and pointing it at another hive's
     # gateway means verifying a leaf signed by a CA generated at runtime,
     # which no build-time trust store can contain.
     #