Fix: Snapshots-Tabelle leer - Top-Level-Datasets initial expandiert

Sub-Datasets (tank/share) waren initial eingeklappt, dadurch waren
alle Zeilen unsichtbar. Beim Laden werden jetzt alle Top-Level-Datasets
automatisch expandiert.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/app/snapshots/page.tsx

@@ -40,6 +40,9 @@ export default function SnapshotsPage() {
       setError(null)
       const data = await api.getSnapshots(dataset || undefined)
       setSnapshots(data)
+      // Auto-expand all top-level datasets so rows are visible by default
+      const topDs = new Set(data.map((s) => s.name.split("@")[0].split("/")[0]))
+      setExpandedDatasets(topDs)
     } catch (err) {
       setError(err instanceof Error ? err.message : "Failed to fetch snapshots")
     } finally {