(feature) add Django detail views for backup runs and snapshots

Add staff-only run and snapshot detail pages so scheduler and command
output can be inspected from the Django UI.

Link dashboard and host detail tables to the new detail views, including
snapshot/base relationships and linked backup runs.

Render stored result and metadata JSON in readable form and cover the new
inspection views with tests.

src/pobsync_server/urls.py

@@ -15,6 +15,8 @@ urlpatterns = [
     path("hosts/<str:host>/discover-snapshots/", views.discover_host_snapshots, name="discover_host_snapshots"),
     path("hosts/<str:host>/retention-plan/", views.host_retention_plan, name="host_retention_plan"),
     path("hosts/<str:host>/schedule/", views.edit_host_schedule, name="edit_host_schedule"),
+    path("runs/<int:run_id>/", views.run_detail, name="run_detail"),
+    path("snapshots/<int:snapshot_id>/", views.snapshot_detail, name="snapshot_detail"),
     path("api/", api.api_index),
     path("api/status/", api.status),
     path("api/hosts/", api.hosts),