feat(panel): reskin backend — node sortIndex, presence/speed, /api/system, credentials, subscription aggregation (Node+Go parity)

panel-go/main.go

@@ -272,6 +272,10 @@ func (a *App) housekeeping() {
 		return
 	}
 	a.getSessions().Prune()
+	// System-status sampling + due external-source refreshes (outside the
+	// transaction; fetches must not hold the store lock).
+	a.monitor().Sample(a.store.Snapshot(), false)
+	a.RefreshDueSources()
 }
 
 // ---------- main ----------
@@ -361,6 +365,32 @@ func run() error {
 		}
 	}
 
+	// Node sort order migration (idempotent): unless the stored
+	// sortIndex values are exactly the permutation 0..n-1, renumber by
+	// storage order. Mirrors the Node implementation's boot migration.
+	{
+		nodes := store.Snapshot().Nodes
+		seen := map[int]bool{}
+		valid := true
+		for _, node := range nodes {
+			if node.SortIndex < 0 || node.SortIndex >= len(nodes) || seen[node.SortIndex] {
+				valid = false
+				break
+			}
+			seen[node.SortIndex] = true
+		}
+		if !valid {
+			if _, err := store.Transaction(func(d *Data) (any, error) {
+				for index, node := range d.Nodes {
+					node.SortIndex = index
+				}
+				return nil, nil
+			}); err != nil {
+				return err
+			}
+		}
+	}
+
 	app := NewApp(store, nil, NewOrchestrator(store))
 	app.replaceSessions(NewSessionManager(app.sessionHours()))