(feature) Add host backup control actions

Turn the host detail page into a more useful operator surface for
starting greenfield backups from Django.

Add quick actions for dry-run and real backup runs, keep the advanced
manual options available, and show whether a host is ready, disabled, or
blocked by missing global config. Surface queued and running counts plus
a direct link to the active run.

Expose requested backup options on the run detail page and cover the new
control flow with view tests.

src/pobsync_backend/views.py

@@ -104,16 +104,27 @@ def create_host_config(request):
 @staff_member_required
 def host_detail(request, host: str):
     host_config = get_object_or_404(HostConfig, host=host)
+    queued_runs = host_config.runs.filter(status=BackupRun.Status.QUEUED)
+    running_runs = host_config.runs.filter(status=BackupRun.Status.RUNNING)
+    active_run = host_config.runs.filter(
+        status__in=[BackupRun.Status.QUEUED, BackupRun.Status.RUNNING]
+    ).order_by("created_at", "id").first()
+    has_global_config = GlobalConfig.objects.filter(name="default").exists()
     context = {
         "host": host_config,
         "schedule": _schedule_for_host(host_config),
         "discovery": inspect_snapshot_discovery(host=host_config),
         "manual_backup_form": ManualBackupForm(initial=_default_manual_backup_initial(host_config)),
+        "can_queue_backup": host_config.enabled and has_global_config,
+        "has_global_config": has_global_config,
+        "active_run": active_run,
         "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(),
+            "queued_runs": queued_runs.count(),
+            "running_runs": running_runs.count(),
             "failed_runs": host_config.runs.filter(status=BackupRun.Status.FAILED).count(),
             "incomplete_snapshots": host_config.snapshots.filter(kind=SnapshotRecord.Kind.INCOMPLETE).count(),
         },
@@ -153,6 +164,7 @@ def run_detail(request, run_id: int):
     run = get_object_or_404(BackupRun.objects.select_related("host", "snapshot"), id=run_id)
     context = {
         "run": run,
+        "requested": run.result.get("requested") if isinstance(run.result, dict) else {},
         "result_json": _pretty_json(run.result),
     }
     return render(request, "pobsync_backend/run_detail.html", context)