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)

frontend/packages/dashboard/src/common.css

@@ -85,6 +85,11 @@ code {
   color: var(--purple); border-color: var(--purple);
   text-shadow: 0 0 6px color-mix(in srgb, var(--purple) 40%, transparent);
 }
+/* Active Claude model badge on dashboard container rows. */
+.badge-model {
+  color: var(--blue); border-color: var(--blue);
+  opacity: 0.8;
+}
 /* Context-window usage badges on dashboard container rows. */
 .badge-ctx-ok {
   color: var(--green); border-color: var(--green);