swarm-otel: collect only the units the swarm's services declare

The journald receiver was configured with a directory and no filter, so
the swarm's log store received every unit on the host that runs the
collector. On a hive whose services live on a workstation that includes
the operator's desktop session, in a store every swarm operator can read.

The receiver has no system-only switch and its `matches` field is an
allowlist too, so what the swarm collects has to be stated rather than
excluded. Each service module names its own units: a service that is not
running contributes nothing, and one added later arrives declared.

An empty list is fail-open — the receiver renders no filter at all and
reads everything — so it is asserted against.

nix/host-modules/swarm-ca.nix

@@ -138,6 +138,13 @@ in
   };
 
   config = lib.mkIf (hyperhiveCfg.enable && cfg.autoConfigure) {
+    # A CA that fails to issue is invisible until something makes a TLS call
+    # hours later, so these two oneshots are worth more than most services.
+    services.hyperhive.swarm.otel.journaldUnits = [
+      "swarm-ca"
+      "swarm-services-ca"
+    ];
+
     systemd.services.swarm-ca = {
       description = "Generate the swarm root CA when absent";
       wantedBy = [ "multi-user.target" ];