swarm-grafana: provision log store and metrics store dashboards

Two more per-service boards, cut from the withdrawn combined services
board: the log store (4 panels) and the metrics store (5).

The combined board was one page carrying panels for four different
services; the seams were already there, so this is a re-cut rather than
new authoring. Each board's subject is one service, and the services
page that remains will carry only panels whose subject is the *set*.

Both were imported by the operator before being committed here, so the
queries are known to draw against the live stores rather than only
parsing.

nix/host-modules/swarm-grafana.nix

@@ -61,6 +61,8 @@ let
         "agents.json"
         "authelia.json"
         "claude-usage.json"
+        "logstore.json"
+        "metricstore.json"
         "queue.json"
       ]
   );