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-authelia.nix

@@ -983,6 +983,13 @@ in
     # bridge at that wrong answer.
     services.hyperhive.gateway.localNames = [ cfg.domain ];
 
+    # The bridge as well as authelia: it is the half that writes the identity
+    # store, and its refusals are returned to callers as a bare 401.
+    services.hyperhive.swarm.otel.journaldUnits = [
+      "authelia"
+      "swarm-authelia-bridge"
+    ];
+
     # Declared here rather than in the collector's module, per the option's
     # own rule: an entry exists only where the service that named it runs.
     #