(feature) show latest snapshot on the Django dashboard

Add latest snapshot context to each dashboard host row so imported legacy
snapshots are visible without opening every host page.

Link the latest snapshot directly to its detail page and show its kind
and status beside the host snapshot count.

Cover the dashboard latest-snapshot selection with a view test.

src/pobsync_backend/views.py

@@ -20,12 +20,18 @@ from .snapshot_discovery import discover_snapshots, inspect_snapshot_discovery
 
 @staff_member_required
 def dashboard(request):
-    host_qs = (
+    hosts = list(
         HostConfig.objects.annotate(snapshot_count=Count("snapshots", distinct=True), run_count=Count("runs", distinct=True))
         .order_by("host")
     )
+    for host_config in hosts:
+        host_config.latest_snapshot = (
+            host_config.snapshots.select_related("base")
+            .order_by("-started_at", "-discovered_at", "-id")
+            .first()
+        )
     context = {
-        "hosts": host_qs,
+        "hosts": hosts,
         "global_config": GlobalConfig.objects.filter(name="default").first(),
         "latest_runs": BackupRun.objects.select_related("host", "snapshot").order_by("-created_at")[:10],
         "counts": {