(feature) Add live refresh for run detail status

Add a server-rendered run detail partial and a small vanilla JavaScript
refresh hook so active backup runs update status, controls, timing, and
rsync log output without a full page reload.

Document the Django-template-first refresh pattern for future control
panel work.

Refs #36

src/pobsync_server/urls.py

@@ -37,6 +37,7 @@ urlpatterns = [
     path("hosts/<str:host>/schedule/", views.edit_host_schedule, name="edit_host_schedule"),
     path("runs/", views.runs_list, name="runs_list"),
     path("runs/<int:run_id>/", views.run_detail, name="run_detail"),
+    path("runs/<int:run_id>/live/", views.run_detail_live, name="run_detail_live"),
     path("runs/<int:run_id>/rsync-log/", views.run_rsync_log, name="run_rsync_log"),
     path("runs/<int:run_id>/cancel/", views.cancel_run, name="cancel_run"),
     path("runs/<int:run_id>/resolve-review/", views.resolve_run_review, name="resolve_run_review"),