fix(services): surface validation errors in add-service dialog

CreateServiceDialog.save() awaited mutateAsync without a try/catch, so a
backend 422 (e.g. base_url missing http:// schema) threw uncaught and the
dialog sat silent with no feedback. Wrap in try/catch, hold the error in
local state, render a destructive Alert above the footer. Reset/onClose
only on success; on error the user can fix and retry.

frontend/src/pages/ServicesPage.tsx

@@ -175,9 +175,11 @@ function CreateServiceDialog({
 	const { data: types = [] } = useServiceTypes();
 	const saveService = useSaveServiceInstance();
 	const [draft, setDraft] = useState<CreateDraft | null>(null);
+	const [submitError, setSubmitError] = useState<string | null>(null);
 
 	function reset() {
 		setDraft(null);
+		setSubmitError(null);
 	}
 
 	async function save() {
@@ -190,9 +192,14 @@ function CreateServiceDialog({
 			secrets: draft.secrets,
 			enabled: draft.enabled,
 		};
-		await saveService.mutateAsync(input);
-		reset();
+		setSubmitError(null);
+		try {
+			await saveService.mutateAsync(input);
+			reset();
 		onClose();
+		} catch (err) {
+			setSubmitError(err instanceof Error ? err.message : String(err));
+		}
 	}
 
 	const selectedType = types.find((t) => t.service_type === draft?.serviceType);
@@ -264,6 +271,11 @@ function CreateServiceDialog({
 						</>
 					)}
 				</div>
+				{submitError ? (
+					<Alert variant="destructive">
+						<AlertDescription>{submitError}</AlertDescription>
+					</Alert>
+				) : null}
 				{draft ? (
 					<DialogFooter
 						onCancel={reset}