(feature) Add staff-only Django dashboard views

Add a small template-based UI for inspecting pobsync state through Django. The
dashboard shows host, schedule, snapshot, and backup run summaries, while host
detail pages show config, schedule, recent runs, and discovered snapshots.

Keep the views read-only and staff-protected, document the new dashboard URL,
and cover the routes with focused view tests.

src/pobsync_backend/views.py

@@ -0,0 +1,55 @@
+from __future__ import annotations
+
+from django.contrib.admin.views.decorators import staff_member_required
+from django.db.models import Count
+from django.shortcuts import get_object_or_404, render
+
+from .models import BackupRun, HostConfig, ScheduleConfig, SnapshotRecord
+
+
+@staff_member_required
+def dashboard(request):
+    host_qs = (
+        HostConfig.objects.annotate(snapshot_count=Count("snapshots", distinct=True), run_count=Count("runs", distinct=True))
+        .order_by("host")
+    )
+    context = {
+        "hosts": host_qs,
+        "latest_runs": BackupRun.objects.select_related("host", "snapshot").order_by("-created_at")[:10],
+        "counts": {
+            "hosts": HostConfig.objects.count(),
+            "enabled_hosts": HostConfig.objects.filter(enabled=True).count(),
+            "schedules": ScheduleConfig.objects.count(),
+            "enabled_schedules": ScheduleConfig.objects.filter(enabled=True).count(),
+            "snapshots": SnapshotRecord.objects.count(),
+            "runs": BackupRun.objects.count(),
+            "running_runs": BackupRun.objects.filter(status=BackupRun.Status.RUNNING).count(),
+            "failed_runs": BackupRun.objects.filter(status=BackupRun.Status.FAILED).count(),
+        },
+    }
+    return render(request, "pobsync_backend/dashboard.html", context)
+
+
+@staff_member_required
+def host_detail(request, host: str):
+    host_config = get_object_or_404(HostConfig, host=host)
+    context = {
+        "host": host_config,
+        "schedule": _schedule_for_host(host_config),
+        "latest_runs": host_config.runs.select_related("snapshot").order_by("-created_at")[:10],
+        "snapshots": host_config.snapshots.select_related("base").order_by("-started_at", "dirname")[:20],
+        "counts": {
+            "snapshots": host_config.snapshots.count(),
+            "runs": host_config.runs.count(),
+            "failed_runs": host_config.runs.filter(status=BackupRun.Status.FAILED).count(),
+            "incomplete_snapshots": host_config.snapshots.filter(kind=SnapshotRecord.Kind.INCOMPLETE).count(),
+        },
+    }
+    return render(request, "pobsync_backend/host_detail.html", context)
+
+
+def _schedule_for_host(host_config: HostConfig) -> ScheduleConfig | None:
+    try:
+        return host_config.schedule
+    except ScheduleConfig.DoesNotExist:
+        return None