Fix fan chart gaps and task durations

audit/internal/webui/server_test.go

@@ -149,6 +149,19 @@ func TestChartCanvasHeight(t *testing.T) {
 	}
 }
 
+func TestNormalizeFanSeriesHoldsLastPositive(t *testing.T) {
+	got := normalizeFanSeries([]float64{4200, 0, 0, 4300, 0})
+	want := []float64{4200, 4200, 4200, 4300, 4300}
+	if len(got) != len(want) {
+		t.Fatalf("len=%d want %d", len(got), len(want))
+	}
+	for i := range want {
+		if got[i] != want[i] {
+			t.Fatalf("got[%d]=%v want %v", i, got[i], want[i])
+		}
+	}
+}
+
 func TestChartYAxisOption(t *testing.T) {
 	min := floatPtr(0)
 	max := floatPtr(100)