feat(dash): show active model badge on agent cards (closes #2069)

Read the persisted model name from each agent's harness state file
(harness/hyperhive-model) and surface it as a small blue badge on
the container row in the SW4RM tab.

- container_view.rs: add `active_model: Option<String>` to
  ContainerView; populated by new `read_active_model` helper that
  reads harness/hyperhive-model; only set when container is running
  (stale model info from a stopped agent is misleading)
- container_view.rs: add active_model to ContainerView literal in
  host_stats test helper
- tabs.js: render badge-model chip after needs-update, before
  reminders; add active_model to the row fingerprint so re-renders
  fire on model change
- common.css: add .badge-model (blue, 80% opacity — informational)

hive-c0re/src/host_stats.rs

@@ -205,6 +205,7 @@ mod tests {
             deployed_sha: None,
             pending_reminders: 0,
             parent: None,
+            active_model: None,
         }
     }