test(dashboard): use relative dates so sparkline test doesn't age out of the 30-day window

internal/server/http/ui_dashboard_sparkline_test.go

@@ -49,8 +49,14 @@ func TestDashboard_HostRowSparklineRendersWithHistory(t *testing.T) {
 	hostID := makeHost(t, st, "h-spark")
 	ctx := context.Background()
 
-	// Two history points → polyline must render.
-	for i, day := range []string{"2026-05-05", "2026-05-06"} {
+	// Two history points → polyline must render. Use dates relative to
+	// now so the points always fall inside the dashboard's rolling
+	// 30-day window (ui_handlers.go: since = now-30d); hard-coded dates
+	// silently age out of the window and break this test over time.
+	for i, day := range []string{
+		time.Now().UTC().AddDate(0, 0, -2).Format("2006-01-02"),
+		time.Now().UTC().AddDate(0, 0, -1).Format("2006-01-02"),
+	} {
 		v := int64(100 + i*50)
 		if err := st.UpsertHostRepoStatsHistory(ctx, hostID, day,
 			store.HostRepoStats{TotalSizeBytes: &v}, time.Now().UTC()); err != nil {