fix: avoid error when AI usage is zero (#19388)

Fixes a bug that prevents the managed AI agent usage from showing in the
licenses page of the dashboard when the usage is zero. Adds a story with
this case as well.

site/src/pages/DeploymentSettingsPage/LicensesSettingsPage/ManagedAgentsConsumption.stories.tsx

@@ -26,6 +26,23 @@ type Story = StoryObj<typeof ManagedAgentsConsumption>;
 
 export const Default: Story = {};
 
+export const ZeroUsage: Story = {
+	args: {
+		managedAgentFeature: {
+			enabled: true,
+			actual: 0,
+			soft_limit: 60000,
+			limit: 120000,
+			usage_period: {
+				start: "February 27, 2025",
+				end: "February 27, 2026",
+				issued_at: "February 27, 2025",
+			},
+			entitlement: "entitled",
+		},
+	},
+};
+
 export const NearLimit: Story = {
 	args: {
 		managedAgentFeature: {

site/src/pages/DeploymentSettingsPage/LicensesSettingsPage/ManagedAgentsConsumption.tsx

@@ -44,11 +44,16 @@ export const ManagedAgentsConsumption: FC<ManagedAgentsConsumptionProps> = ({
 	const startDate = managedAgentFeature.usage_period?.start;
 	const endDate = managedAgentFeature.usage_period?.end;
 
-	if (!usage || usage < 0) {
+	if (usage === undefined || usage < 0) {
 		return <ErrorAlert error="Invalid usage data" />;
 	}
 
-	if (!included || included < 0 || !limit || limit < 0) {
+	if (
+		included === undefined ||
+		included < 0 ||
+		limit === undefined ||
+		limit < 0
+	) {
 		return <ErrorAlert error="Invalid license usage limits" />;
 	}