otel: ship the journals the dashboard can already show

The dashboard's log surface is an allow-list: the four harness units in
every agent container, the hive-ci / hive-forge / hive-matrix machines,
and three host units. `swarm.otel.journaldUnits` only named the host
three plus forgejo — so the units an operator can read in the UI were
absent from the store they are supposed to be queryable in, and nothing
reports that, because a name that matches nothing is not an error.

Adds the four agent units, the CI runner and the homeserver. The agent
units are declared by the hive-c0re module rather than by the
agent-modules that define them: those are a guest evaluation and cannot
reach a host option.

Closes #3818

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

@@ -139,9 +139,21 @@ in
     # The daemon that owns every container on this hive, and the helper it
     # delegates its root operations to. An agent asking why a container did
     # not come up is asking about one of these two.
+    #
+    # The four agent-side units are named here rather than by the
+    # `agent-modules/` that define them, which is the one case where "a
+    # module names its own units" cannot hold: those modules are evaluated
+    # inside the guest, and this option belongs to the host. This module is
+    # the host's only knowledge that agent containers exist at all. They are
+    # also exactly the units the dashboard offers as journal filters, so
+    # without them the store cannot answer a question the UI can ask.
     services.hyperhive.swarm.otel.journaldUnits = [
       "hive-c0re"
       "hive-priv"
+      "hive-agent"
+      "hive-mcp-http"
+      "hive-bash-daemon"
+      "hive-matrix-daemon"
     ];
 
     assertions = [